Iceland has said it will continue to accept the old round pound until the end of October, despite the coin ceasing to be legal tender from midnight on Sunday.
The frozen food retailer, which has more than 880 stores in the UK, said it will continue to accept round pounds as payment until October 31.
This will apply to all Iceland and The Food Warehouse stores in the UK, it said.
After October 15, businesses can stop accepting the round pound and they will not be able to give it out as change.
Tesco and Poundland have also previously said they plan to give shoppers an extra window of opportunity to spend up their old round pounds after October 15.
Tesco has said it will allow customers to pay with the old-style coins for a week after the October 15 deadline.
Poundland has said it will be accepting round pounds until October 31.
Major banks have said their own customers can continue to deposit old round pounds into their accounts after October 15.
People can also continue to deposit them into any of their usual high street bank accounts through any post office.
Iceland group managing director Tarsem Dhaliwal said: "We have been ready to accept the new pound coins since they entered circulation in March and all our trolleys have been converted to accept both new and old-style coins.
"However, it is very clear that hundreds of millions of the old coins remain in circulation just three days before the Royal Mint's deadline.
"We are keen to help our customers by making it possible for them to spend them in our stores rather than having to take them to a bank."