Most currencies have relatively random currency denominations. They have a one, many have a two, a five, a ten, a twenty (or twenty-five), a fifty, and a hundred. Added to this is a variety of coins.
So here's how you properly denominate a currency:
First, you get rid of the stupid decimal. Make all of the currency have whole numbers. Just make the lowest four or five into coins.
Second, you minimize the number of notes needed in transactions--so no transaction will need more than a single bill of each denomination is needed.
Thus you would need a $1, and a $2 (so you wouldn't need two $1's).
You can get three with a $1 and a $2, but you can't make four, so you would need a $4.
Five, six, and seven can be accomplished with the bills you already have, but you would need an $8 to go farther.
Can you see the pattern? 1, 2, 4, 8, 16, 32, 64, 128. Those are the denominations we need, and only two of them are included in anyone's currency.
Of course, people would complain that it requires too much math, but how else are you going to cheat tourists?