If your listings are receiving payouts in several currencies, Metrics will convert all of your data to one currency for you.
There is an option available to change which currency is displayed. Scroll to the bottom of the Metrics sidebar to find "Settings and Scheduling". There you'll have the choice to select any one of the currencies that you accept.
If you have one listing, or if your listings portfolio is only receiving payouts in one currency, Metrics will only be able to display that currency.