Throughout the site you can browse in any currency you prefer.
But when you move to the Checkout page, the currency will change back to the
default option used during the setup of the store. The reason for this is purely for
transactions, economic and logistic operations. There is not any actual
increase on the amount to be paid. It is only displayed in different currency
than one you may were using. Feel safe to complete purchase and as you can check there is nothing to hide and there are no hidden fees.