Scenario: Customer purchased items with CASH and had to return some of the items, the items have to be returned to your inventory and handled properly by Point of Sale so the order should be opened and the items applied with negative quantities. 

The negative quantities create a negative dollar total for the item(s), the sales tax amount will also be properly credited and all inventory details will be properly tracked.

Prior to Printing and Billing that negative (return) sale - make sure the terms are "CASH" 

Select the payment option of "Cash"

This will create a negative CASH entry on the deposits screen

Give the customer the Cash and deposit the CASH entry either to Petty Cash or with your other CASH entries that day to balance out the deposits.

The Key to returns is to have the items 'returned' properly at the Point of Sale, there are several tools to make returns easy at Point of Sale for more information please refer to http://help.pluss.co/HELP/PTM%20Vision%20Help/default.aspx?pageid=customer_statements#pageid=history_search_to_return_part