Add coins and banknotes to Currency

We could add the possible coins and banknotes to Currency. For example for Euro (EUR) we have the following:
- Coins:
  - Freq Used: €1, €2, 5cent, 10cent, 20cent, 50cent
  - Rarely Used: 1cent, 2cent
- Banknotes: 
  - Freq Used: €5, €10, €20, €50, €100
  - Rarely Used: €200, €500

Is this useful for anyone and how would they want to use it?
