Multi-Currency - integrated with Bold Cashier - gives your customers the flexibility to check out in the currency of their choice. They can select which currency they wish to view on the storefront, and pay in that currency when they reach the checkout.
Note: This integration requires that both Cashier and Multi-Currency are installed and set up on your site. You also require an attached payment gateway that can accept your customer's currency, in order for them to pay in that currency / pay with those funds.
However, store owners utilizing a custom domain for their site need to have their own SSL certification. The currency information does not get passed correctly to Cashier's checkout when a site is using BigCommerce's default shared SSL. A paid, private SSL for your domain is required to maintain a selected currency throughout the site.
Visit BigCommerce SSL Certificate (links to BigCommerce's Help Center) for more information on how to obtain a private SSL.