Order Total modules allow you to add fees or discounts to the subtotal and thereby increase or decrease the total charge for the order.
They appear on the screen shown when you click Admin > Modules > Order Total.
As of Zen Cart 1.5.7, the built-in order total modules are:
For more information, see the order total FAQs.
See the Managing Modules FAQ for information on Installing, editing and removing order total modules.