You do get those Coinstar machines which do that though they charge about 10% commission.
With the Coinstar in my local Tesco you used to be able to use the printed voucher at the checkout. Now regardless of details on the machine you have to get cash back at Customer Services. So put in coins that total say £3.79 after commission and the fewest you can get back is £2 + £1 + 50p + 20p + 5p + 2 x 2p - rather silly.