A discount can be applied to an entire Sales Order, even if other custom pricing has already been used. This can only work if % line discounts has been selected.
To apply a discount to an entire Sales Order:
1) Locate the Sales Order from the Sales Order Ledger or use the Find with in the Sales order.
2) Click Modify. The order cannot be discounted unless it is being edited.
3) Select the Discount Order option from the Actions menu, as shown in the following screen.
4) Enter the "Discount %" and click OK to update all order line items.
NOTE: You can also clear all line item discounts by entering 0% using the Discount Order action.
The discount will be applied to all order lines, as shown in the following screen: