AlanB: You say- "And as large as that minor blackmarket might be, not worth spending millions chasing thousands? But rather aimed at multinationals, many with budgets larger than sovereign nations, 40% of whom pay no company tax to anyone!"

Do you really think multinationals wouldn't be able to "engineer" a way around your proposal? Do you really think that you've outsmarted them?

Generally, for most multinationals*, if it is good at making money, then there is one very, very, very easy way for a government to get it to share the spoils with them. This scheme is not at all new and doesn't involve any new laws nor taxation measures and is implementable straight away. In fact many people (including quite average ones- like me) use this method all the time!! Can you guess what this could possibly be?
*this method applies to many, but not all multinationals. If can be successfully applied to most of the multinationals that I've heard accused of not paying enough tax- like Apple for example.

Multinationals need to move money, that means banks, international transfers and remittances. And an unavoidable expenditure tax could claim a fair and equitable percentage of those repatriated profits from Australian earned income, before it made it to the tax havens! Thereby defeating the rationale for needing to shift money earned in Australia anywhere else!

Moreover some exceptionally imaginative accounting practise has money chasing its tail through a number of sister companies, to create various financial illusions!?

And just one of many creative accounting strategies to rob the tax office, or create an appearance of elevated cash flow in order to secure funding. And Legalized fraud?

Yes the multinationals can be beaten by simplicity and accompanying transparency, almost impossible to defeat and by making paying your share of tax less expensive that the cost of convoluted creative accounting!

Only possible due to antiquated multilayered convoluted tax laws, with a loophole on every page! Only failsafe simplicity has any chance of ending endemic avoidance, which also serves a few quisling Australians!

So why would anyone try to cheat at the other blokes expense! And why should honest Australian taxpayers be expected to pick up that slack?

If you think that's too clever, let's try something not yet ever tried! I mean 50% of something is always going to be better than 100% of nothing!

If the tax avoiding multinationals don't don't like having their avoidance schemes removed via transparent simplicity! Tough! And it would be a David and Goliath struggle! And guess who won that encounter!? You guessed it, the shepherd with the ultrasimple sling shot!
Alan B.

AlanB: You very first sentence- "Multinationals need to move money, that means banks, international transfers and remittances. ", with the implicit assumption that you mean *Australian* banks then this is where you're going wrong. This is a false assumption from the start. To severely reduce the effectiveness of your system the Multinationals can use various strategies, for example, only do business in foreign currencies with foreign banks (with the Internet and the various online financial services available these days even requiring the general public to buy with a foreign currency doesn't cause to much pain- many people already buy stuff online from overseas in foreign currencies, I've done it myself.)

But let's for the sake of argument pretend that your system cannot be side-stepped and is implemented. Let me show you an obvious glaring problem that you overlook. Specifically, what the impact of a 5% tax on all money transfers means to prices.

Take a loaf of bread at your corner shop for example. To produce this loaf of bread in Australia let's say that the farmer sells wheat to an agent, who sells it a miller, who sells the flour produced to a wholesaler, who sells it to a distributor, who sells it to a baker, who sells the bread produced to a distributor who sells it to the corner shop. So here we have 7 transactions each adding a compounding 5% to the price which is a lot more tax that what is currently paid on a loaf of bread.
But what makes this situation even worse, is comparing the tax paid on goods produced overseas to those in Australia. Because when a good is manufactured overseas then your 5% is not paid on every intermediate step of production but only on the steps incurred from the importation (ie: the import purchase and the local distribution). This greatly disadvantages our local producers/manufactures.

By-the-way: I'm still waiting for you to try to guess at my very simple way to get multinationals to pay a share of their profits.

Alan B.

Have you ever heard of tax deductions?

thinkabit
"By-the-way: I'm still waiting for you to try to guess at my very simple way to get multinationals to pay a share of their profits."

I give in?

Jardine K Jardine: answer- buy shares in the company then they willing give you a slice of the profits!

For example, if the USA government wanted 30% of Apple's profit they could just buy 30% of the company.

To be fair. I should really correct myself a bit- companies aren't required to return all the profit to the shareholders. Indeed some industry types, such as technology companies quite often hold onto a lot/all of their profit. But when then don't release dividends the company retains the wealth for further investment so the shareholders gain anyway (well theoretically anyway).

I should also clarrify that I'm not advocating the forced nationalization of companies. Nor do I support the notion that if a government bought into a company then it should involve itself in the running/direction of the company. I certainly don't believe that government can manage business better than private enterprise-except in certain particular instances.