Short changing on returns - something wrong with this policy

Returned an item which only cost R12.67 & replace with the correct item. The refund was R12.60 & I'm sure I'm not the 1st customer to notice this and question the person. Yes only 7c but 7c from each customer. Why don't they round up like other retailers when it's over 5c, but I guess they found another way to make a few bucks.