A lot of places that accept Bitcoins use BitPay and get paid in US dollars. BitPay charge a 3% fee for this service. (You can accept Bitcoins and exchange them yourself but then you take on the exchange-rate risk, which is quite substantial given how much the Bitcoin exchange rate varies.)
They must've changed it at some point and I only found outdated information, sorry. As wmf points out the total fees are actually 2.69% once you take into account the 0.99% fee for the payment gateway part.
BitPay charges a fee to accept BTC and another fee to convert to USD; these add up to 2.69%. If the customer pays Coinbase 1% to convert USD to BTC then total fees are nearly 4%.
