This is what Bitpay does. You, the merchant, can accept bitcoin (and other currencies) using Bitpay's payment system. Bitpay immediately credits your account

This is what Bitpay does. You, the merchant, can accept bitcoin (and other currencies) using Bitpay's payment system. Bitpay immediately credits your account with USD. No risk of long-term (more than a few seconds) price moves in BTCUSD. The downside is that Bitpay, like every other authorized cryptocurrency "bank", is crippled by KYC/AML regulations and cannot process all the applications they receive for new customers.