Magento is a e-commerce CMS. Sometimes, client want to allow multiple currencies and give their customer the options to select their currencies.
By default magento has the feature to allow multiple currencies and change currency options for customer from magento frontend.
Now you can easily do that by following the below step:
First Login as admin to your magento admin panel and go to “System->Configuration”
And then select “Currency Setup” tab and then set up your base currency and select other currencies that allow from “Allowed Currencies” and then save this configuration.
Here you give manually currency rate and also can import currency rate. After giving currency rate save the configuration and then refresh your magento frontend.