Hello,
I also had such a request from my customer. It can be solved by setting. The procedure is as follows:
1. In module Pricing/ Register Item formula set discounts on Group Items. To column % enter a value for example: -7.
2. Create an item with description Discount 7%, to field on Item /flip Pricing/ field Item Formula paste special item formula from first step.
3. On Invoice or Sales order add several lines of items from group item specified in item formula.
4. After entering items insert item Discount 7%. Item automatically will calculate discount.
Pavel Andok
Partner HansaWorld in Slovakia