If outside the US, you also want to look at dynamic currency conversion (DCC) as that will compound the problem, which is basically the merchant converting the charge to another currency (yours) for your convenience, but at less favorable rates than if you allowed your credit card company to do so.
The simple rule on this is: if a foreign merchant offers to process your CC transaction in USD or the local currency, always pick the local currency! If they don't offer, make sure to ask for it anyways! The POS device will have a much worse exchange rate than your CC that offers no FTF.