Go to System > Configuration > General > Currency Setup > 'Currency Option'
1. Base Currency - In this dropdown select set base currency which is used in our store. Base currency is used for all online payment transactions.
2. Default Display Currency - In this dropdown select display currency which is display in store.
3. Allowed Currencies - In this dropdown select which is allow for payment.
These step set currency for our store.
Fill all option click save config button for save setting.