No they do not
No, and yes. You can't just walk in with euros and exchange for dollars. You can however, provide euros as payment for your purchases and the register will automatically exchange it for you. Canadians do it all the time with their dollar at this location. It's a Walmart so they are connected to the main office which takes pretty much any exchange.
I am not sure but you could call the Walmart store near you
They have money gram to send and receive money. They don't exchange currency.
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