If there's a head tax of three quatloos per year, then I have to get three quatloos every year. So does everybody else. That creates a value for quatloos, no matter how useless they otherwise are.
On the other hand, if it's an income tax, something like "How many quatloos did you make this year? Send in one-third of them", and I didn't make any quatloos because I use some other kind of money, well, I owe exactly zero quatloos (until the government figures out the loophole and, worse, fixes the exchange rate).
On the other hand, if it's an income tax, something like "How many quatloos did you make this year? Send in one-third of them", and I didn't make any quatloos because I use some other kind of money, well, I owe exactly zero quatloos (until the government figures out the loophole and, worse, fixes the exchange rate).