[impeachgod]

Actually, in the Soviet Union you used to have 3-kopek and 15-kopek coins, as well as 3-ruble notes.

[listic]

Clarification: late Soviet ruble (1961-1991) had the following coins: 1, 2, 3, 5, 10, 15, 20, 50 copecks and 1 ruble http://en.wikipedia.org/wiki/Soviet_ruble

I think if you really want to minimize the number of coins per transaction, you can always add more (than four) denominations of coins, up to some reasonable number.