Can I add discount on total bill?
Yes, you can add discount on total bill.
1.First enable setting Enable Bill Discount in Percentage and Enable Bill Discount as Fixed Amount(If you want to gives discount in fixed amount)
2.Go to Setup > Configuration > Inventory Setting.
3.In sale transaction you can see Item Discount box at the bottom .
4.You can add either percentage discount(%) or amount discount(Rs) on total Bill.
5.Click on OK/Apply button.