You can add a standard discount into your system, which can be assigned to charges as needed. Discounts can be percent discounts, dollar amount discounts, or some combination of both. If a combination, the dollar amount discount will apply first, with the percent discount applied to the new, lower total.
Important Tip: Normally, defined discounts will automatically apply a fixed percentage and/or dollar value discount to a charge. However, if you want to create a "flexible" discount, which allows you to specify a variable value at the time it's applied, simply create the discount definition as normal but leave both the Discount % and the Discount dollar-value fields as "0" and "0.00" respectively). When applied, this discount will prompt you to enter the dollar value of the discount.
To add a new discount, go to the Admin drop down menu, select Manage... then Discounts. This will bring up the Manage Discounts pop up. Select the green +Add New Discount button.
Discount Name (text box) - the name of the discount that appears in the Discount drop down menu on the +Add a New Charge pop up.
% Discount total charge by this Percent (number) - the percentage applied to the discount. Leave blank if a dollar amount discount is preferred.
Discount total charge by this dollar value (currency) - the total dollar amount discounted from the charge. Leave blank if a percentage discount is preferred.
Description of this discount - a description of the discount for administrative purposes.
To edit a standard discount, select the discount from the Manage Discounts pop-up (Admin->Manage...->Discounts). Change the details and finalize by pressing the green Edit This Discount button.