There is a limit to how many coins you can use to pay for something.
Did you know ? “Many South Africans wonder if the 10c and 20c pieces are still legal tender. They are and should be accepted as payment for any goods and services. However, there are limits to how many coins may be used per transaction.” – The South African Reserve Bank
This limit is at the discretion of the retailer. A company cannot refuse your payment if it falls within the limits but they can also choose to ignore the limit and accept more coins. Should a place refuse your legal tender. The bank says you should stand your ground and ask for the manager if the teller does not wish to assist. If the company still refuses to accept the coins, you can report them directly to the Reserve Bank.
SOURCE https://www.goodthingsguy.com/opinion/south-african-coins/