X Tape Z Tape

I'm building a database for my retail store.
Employees will enter sales in a form that will calculate and reconcile the sales during their shift/time.
Their may be 4 "x tape’s” run in a day that will have a running total for the day as in...
10AM . x#1101 . employee #1 . sales of $100.00
1PM . x#1102 . employee #2 . sales of $250.00 (employee #2 sold $150.00 between 10am and 1pm)
I need the ($100) prior sales (prior sale are called “Pulls”) for any period to show and be calculable on the form for each employee to be able to reconcile their draw.
When the z tape form is run the Prior sales/(Pulls) are back to zero.

Please help