Donation Store can display it's prices in a huge list of different currencies. To stay up to date and current with all of the exchange rates it uses the Open Exchange Rates API. Open Exchange Rates offer free, current and up to date exchange rates to all users. They do offer paid plans, but this is for larger websites.
The free plan offers hourly updates and 1,000 API requests per month. If you feel like your network will have more requests then that, we recommend buying one of their plans. If you do not want different currencies, you can remove the option of selecting a currency on your webstore and just stick to the default currency.
To get your App ID, simply create a free account at OpenExchangeRates.org
After that, simply click "Grab your App ID."
Now copy and paste this App ID into the Donation Store installer.