I don't know about USD accounts but when I was sending my donation to HtheB, I tried both. Using GBP, my nominal currency, PayPal wanted to charge me £0.10. Using EUR, it did not charge me anything. I took a note of the exchange rate and it was the same in both cases. So I went for sending in EUR. The recipient received what PayPal said they would receive, so I assume it did not charge them anything either.