The User & Usergroup Discounts module ships with the Commerce core as of v0.12. Enable it in Configuration > Modules.
Once enabled, you can manage user and usergroup discounts from the new "Discounts" top menu.
User(group) discounts are always a percentage of the order total, applied to each individual order item.
User and user group discounts can be restricted to:
- Specific products
- Date/time-based availability
- Min/max order totals
When a user(group) discount is available to the logged in user, it is automatically applied to the items in their cart.
If multiple user(group) discounts are valid, they will all be applied.