I'm try to use the case conditions statements to calculate the sales, but I got stuck.
S_Regular Price is a summary of Regular Price.
S_Discount is a summary of Discount.
S_Custom Price is a summary of Custom Price.
Regular Price is hard coded.
If the cashier enter a Custom Price, then the Regular Price will be negate.
So the Custom Price add the S_Discount to the Subtotal.
If not, Subtotal = S_Regular Price - S_Discount.
Here's my current calculation:
Case(S_Custom Price = ""; S_Regular Price - S_Discount; Custom Price ≠ ""; Regular Price - Regular Price + S_Custom Price - S_Discount + S_Regular Price)