In my D&D campaigns, I got sick of everything being a multiple of 10, when historically coins were multiples of 12, 4, 6 etc. Just consider the British penny; half-penny; farthing (four to the penny); threepence; groat (four pence); sixpence; shilling (equal to twelve pennies); florin (two shillings); half-crown (2 shillings and sixpence); crown; pound (20 shillings) and guinea (21 shillings).
There is also the oft remarked upon fact that in the D&D world, everyday items are greatly inflated in price, with every thing being held to the d20 ‘gold’ standard.
To that end, I created a more varied system. The campaign that uses this is set in Middle-Earth, and for the currency of the North (the ancient realm of Arnor), I created a system with more reasonable values (a standard working wage of a penny a day) and a wide variety of coins, from different races (Human, Elf and Dwarf) and regions.