Cant get the lock sale receipt with separate service charge with total amount

I have a restaurant and when the customer ask for the bill i want to give them a receipt which shows the total amount  of what they purchase before they pay, so i use lock option to print that receipt , problem is this receipt includes prices of each items including the service charge and that's not i want it to be, i want the service charge to print separately with total amount, but i couldn't find a way to edit this. If i cant change it i cant use this software, because when customer see this they get bit confused when they see the price is different from menu, then we have to explain that it includes the service charge, please reply if you know the solution for this ASAP