We do not have a way to show that. For example if you charged $100 per hour. If you give a 5% discount, what would you do? Would you change the Rate to $95? Even if you did, the client would not know it's a "discount". I will add your request to our "wish list", but I cannot say if this would get implemented or not. We do have Discount for the whole invoice and that indicates that there is a discount, but cannot do it line by line.