This seems like a situation where the choice of names is misleading the design thinking. In this case, I would first list out the different terms that are used in the problem domain, which I would bet is about denomination equivalence and/or conversion. Terms would include currency, base
unit, coins or coinage, bills or banknotes, and denominations. For example, in the US, coin denominations are the penny, nickle, dime, quarter, half dollar, and dollar. The base unit for US currency is the dollar. The base unit of currency in Singapore is also a dollar but with different coin denominations: 5, 10, 20, 50 cents, and $1.
With this in mind, I would then start trying to solve the larger problem at hand, which is still not quite clear to me, rather than trying to model the currency and denominations as enums up front. This will probably give me a better sense of how I would like to use currencies and denominations in the problem domain.
So again, how exactly are you planning to use these classes and enums? What is the context here?