The currency of the Greater Lands is as follows:
1 Gold (Coronas)= $100
1 Silver (Mirrors)= $10
1 Copper (Dusts)= $1
Anything below that is handled by cutting Dust down into "Grains," and the divisions by which a person may divide the peice are marked on the coin. It's only legal to cut Dusts, not Mirrors or Coronas.
The monetary system of the Lesser Lands is similar in that it is decimal, though conversions of course depend on where, who, and why you are converting your currency. Additionally, many kings mark their currency, making it worthless (or simply worth less) in rival kingdoms.
1 Obsidian (Blacks) = $100
1 Jade (Greens) = $10
1 Iron (Grays) = $1
Anything smaller can be bartered for with glass beads, which are an unofficial folk currency.