Site Currency
Site currency is the default currency selected for the site. Whenever an order is created, currency selected in the site will be considered.
To Define Site Currency
Access Site Edit window.
Click on import button available in the Currency Field.

R2 will display the Currency Code list dialog box with existing currency code definitions.

Double-click on the desired currency code to select as the Site Currency.
The selected currency code will be displayed in the site-edit window.

For more details on Multi-Currency feature in R2 click here.