One additional motivation is a historical approach to reduce losses due to employee theft. In a cash economy "rounder" numbers would make it easier for employees to take payment without having to ring up the transaction on the till. For example if a magazine was offered at a price of $5 the employee could simply ask for the $5 from the shopper who is more likely to have a $5 bill on hand, the exchange of goods for cash could then take place with the employee pocketing the money and the customer walking away having happily made he purchase (not necessarily aware of the employee's malfeasance). If the goods purchased are not nice round numbers, there is more of a likelihood that the customer will be more invested in the transaction being run up in order to get their change from the transaction.