I like Nac's idea.
Also, I have a currency from a book I was starting, but I could gladly donate.
--==--
Ordered by value, from highest to lowest:
Datra – The highest valued and largest coin (one and 1/4 inch diameter) in the Imperial Trade System. It is made of pure gold, and is usually only found in the possession of nobles; if peasants had them, they wouldn’t be peasants.
Grutz – The second highest-valued coin in the Imperial Trade System. Smaller than the Datra (one inch diameter), and made of pure silver.
Darna – Slightly larger than the Itei (13/16 inch diameter), and possesses a higher value. Forged of a metal called “Gustavian Silver”, after the Vesbold who first discovered the alloy; Antonin Gustav. The alloy is a mix of equal parts silver and tin, finished with a silver leaf brush.
Itei – A relatively small coin (3/4 inch diameter), formed of an alloy of bronze and nickel, and holds more value than the Klau.
Klau – A small bronze coin (half an inch in diameter) of low value in the Imperial Trade System.
One Itei is worth twenty Klau.
One Darna is worth five Itei or 100 Klau.
One Grutz is worth fifteen Darna, 75 Itei, or 1500 Klau.
One Datra is worth ten Grutz, 150 Darna, 750 Itei, or 15000 Klau.
--==--
Just disregard the "Imperial Trade System" scattered throughout. Or don't, if you like it.
Let me know if you like the idea.
EDIT-1: Also, ignore "Vesbold". It only works in my book.
EDIT-2: I realize Korah already suggested a system, but I'd still appreciate a critique of mine. Good, bad, whatever. What do you like, and what do you not like?