The Sales Aggregation screen displays sale values in USD currency by default. You may change the default currency to the one used when sales happen. Changing the default currency here saves it for future use.
You may also change the default Sales Aggregation currency in the My Settings screen, Global Report Filters tab. Click the down arrow to the right of your name, choose My Settings, Global Report Filters, and go to the bottom of the screen to access Sales Aggregation currency settings.
The Sales by Currency chart always displays sales in the currency the sale occurred. Other charts update sale values to the selected currency.