Website Customers and Multiple Currencies
Shoppers can place orders through web store checkout only in their primary currency.
When a shopper places the first order and registers on the website, the currency of that order becomes the customer's primary currency on the customer record.
Customers who register but do not order can select their primary currency during registration.
You can add transaction currencies for a customer, but those currencies are available for use only through the My Account section of the Web store or through the Customer Center.