Although you can set a % discount at customer level, you may find that this does not give you the direct control you need. You may want to individually price certain items for a specific group, so for example it might be $15.00 for retail customers, or $13.25 for wholesale clients.

Kartris has a tab under versions labelled 'Customer Group Prices' where you can override the price of any version for each customer group. Leaving the price at zero for any group will mean that the item for that group will be at normal price (and not zero!).

Of course, this functionality can enable you to have customer-specific prices too - you can create a customer group and assign just one customer to it, and then set prices for that group.