Interesting question. Most times fantasy writers just go straight to 'gold' and keep it at that
Since Enderion has been partially united, at least, in the fourth age, by the Congress of Enderion, there is a currency similar to the Euro. It has strong value and is all coinage (although paper I.O.U's are sometimes accepted at certain places).
That being said, this is still an entire world; and its far from perfect. There are many, many more currencies than just that one out there. On Flerré, each nation also has many of its own coins (which are base six instead of base ten as the international ones are, thus adding to the confusion) in circulation. The Petathoran nations use whatever coins of whatever nation on Flerré colonized them.
In Al-Diurina, things are similar to Petathora. Each nation uses the currencies of the nations of Tbuga (which invaded Al-Diurina in the first age). In Al-Diurina, however, where the Congress is based, use of the international currency is highest. The dwarves use their own currency and do not use the international standard.
Tbuga is the savagest of the four continents, where the humans are the least 'civilized' (although its the original location of the species), and does not use anything but their own crude coinage and some international stuff.
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On Nadrae, the men on the islands use the currency of Nerandia (since destroyed) and do not know about the Congress. The aquaeria people use a barter system adapted to their undersea environment.

Sorry for rambling...
eruheran