In the interface’s Properties panel (3rd panel), you can apply a quantity discount to a product by entering the quantity and the relevant amount or percentage discount.
To specify a percentage discount, just add “%” after the entered value.

In the Products panel, in “Prices” view, the “Discount Price” column shows all the applied discount rules in the following text format:
2:10.00%_6:48.00%_19:19.00%
Quantity:Discount _ Quantity:Discount _ Quantity:Discount _ ...
Bulk Editing Discount Prices
To apply a rule quickly to several products:
1. Right-click on the cell containing the rule and select “Copy”.
2. Select the desired products, right-click in the Discount Price column and select "Paste 2:10.00%_6:48.00%_19:19.00%"