Tracking My Employee's History Of Changes.

I am using excel as point of sale book (to record customer name, service, and total price etc.) at our hair salon. We have employees that may be there to manage alone from time to time, and enter clients into excel.
Our worry is straight forward, and involves them erasing what they wrote. I am confident that the actual service and price is entered at the beginning, but want to track their changes to their own entries.

The "track changes" would work if it "tracked changes" after entry. But it seems to track the last change from saving. For example....the employee enters $40.25 presses enter--after she knows she can get away with a change, she may erase it altogether or change it to say $16.75.