Path in CC5: System settings - Contracts - Currencies
Here you get an overview of available currencies in the database. Fixer.io is the source, and the exchange rates are updated every night.
To activate a currency from the register, click Edit and then check off Set as available. Select the Statistics tab to see the historical exchange rates.
Other sources can be added as required, either by currency codes or manually. Select New currency, give the currency a title, such as "Euro", add any currency code, such as "EUR", select the number of decimal and thousand separator to use (comma/period) and add a symbol, such as "KR". Manual, date-managed exchange rates can also be added by selecting Add manual rate.