Symptoms
When using multiple locales, you can specify an exchange rate to be used when calculating prices in different currencies. When you specify an exchange rate for Euros through the Currencies page on the admin site, that exchange rate is not applied if the user selects EUR (Euro) from the currency selection box while viewing products on the site.
Cause
This behavior is by design. The store will always use an exchange rate of 1.00 for the currency code specified in your Localization.CurrencyFeedBaseRateCurrencyCode AppConfig regardless of what the exchange rate is set to via the currency page.
Solution
The Localization.CurrencyFeedBaseRateCurrencyCode AppConfig should be set to match the currency used as the base for your currency calculations. For example, if your store’s base currency is U.S. Dollars (USD), this AppConfig should be set to USD as well.