What a great infographic product design idea!  From designer Mac Funamizu on his site, PetitInvention, Infographic Coins that use the physical analogy of a pie chart to help consumers figure out the currency, especially when visiting a foreign country.  You have to ignore some of the benefits of all round coins, but the idea is spot-on.  Feeling in your pocket, you could almost always pull out the right coin.

The round shaped coins must have a lot of benefits that other figures such as a triangle or a square don’t. Also, non-rounded coins may have many demerits. Aside from those, travelers and other people who are not accustomed to the currency would be able to easily remember how much each of these coins is (as long as she knows how to read pie charts).