Our approach has been to add a price field for each pricing level and then use rules based on user role to set the price for each product ( if the pricing level has a value in it ). Retail is just the default price that everyone starts at, it only gets overriden if required.

You may need to make sure your rules weights are correct to apply them in the right order. If a user has two of the roles used in pricing then they should get whichever one you think is appropriate. eg if a user has both wholesale & distributor roles then distributor should be applied last.