Can we subtract a value to the total amount of a payment in zen cart?

I have a zencart web site in which I need to subtract so开发者_如何学Cme amount from the total value of the payment befor going to the paypal site to pay it. Can I do that in zen cart? Is there any plug in for that?

Take a look at Group Discounts - this shows you how to reduce the total value of the cart by a percentage for certain groups; you could base your price reduction on this module.