There are probably similar rules in other countries.
Also handy for reducing transfer taxes on house purchases - you can have a higly qualified QC (fancy lawyer) swear affidavits that they witnessed the purchase of a house for an absurdly low amount and therefore the required tax is correct despite being so low.
If a seller offers a house for $6,000,000 and an offer is made to pay $200,000 in legal tender of that country .. and the seller accepts ... what is the sales tax?
Is it calculated from the $200,000 in legal tender which was witnesed by officers of the highest standing, or is it calculated from the metal value of the coins ($6 million)?
You really don't want a tax advisor on this, you want an authoritive legal opinion.
It is a loophole that has been exploited in various countries at various times - but you'd want to be sure of current laws if you're tempted to go that route.