Currency on The Sea of Storms is based on Andoran weight coins as explained by Robert Jordan on http://www.tor.com/jordan/questions.html.
What is the currency break down for Wheel of Time? How many coppers make up a silver penny? How many silver pennies equal a silver mark? How many silver marks make up a gold mark?
Robert Jordan Answers:
This varies from country to country, along with the sizes and weights of the various coins, the reason that bankers and others - such as Bran al'Vere - use scales for comparing coins. The heaviest coins in weight of precious metal come from Andor and Tar Valon. For the coins of those two, the scale is very simple.