Would you like to have different currencies at your store but leave only some of them at checkout? Let your customers visit your store in a different currency than checkout and avoid them to convert it to their local currency.
Your customer can visit your store in any of the defined currencies at your store so they do not have to convert currencies. They can visit your store in their local currency and they will feel more comfortable. When they get to checkout, if customer has a different currency that the ones allowed, it will be automatically changed to the one that you selected so payment will be available only in one of these currencies.
Demo : https://addons.prestashop.com/en/registration-ordering-process/8913-force-currency-at-checkout.html