..none of the large supermarkets allow tipping of any kind, if you feel you have recieved good service from a particular member of staff, what you can do is write to the store telling them how helpful he/she is , he/she will more than likely be given some reward points ( which he will be able to redeme in store) depending on the scheme ran at that particular store... most people will queue/write /phone to complain about bad service, but hardly anyone bothers to comment when they have recieved excelent service...