Order total discount in ubercart?
Commerce Discount Extra


  Provides a number of common discount condition and offer types:
  
  Order discounts
  
  Condition types
  
  
  Order-owner role
  Total items in order
  
  
  Offer types
  
  
  Fixed amount per-quantity discount (Buy X product get Y (or X)    product at discount up to some number of (or unlimited) times)
  Percent per-quantity discount
  


Ubercart Discount Coupons


  A checkout pane, a cart pane and a block are available for customers
  to enter coupon codes, each of which can be enabled or disabled
  separately. Discounts can be shown as an item in the cart or applied
  on the checkout page.