Yes, the price rules will handle this nicely.
Go into the Price Rules module, create a Platinum Price rule with the discount you would like to offer, and then assign only to the Platinum Rule role and they will see the pricing when they log in. Do the same as the other roles.

I have used this successfully for many clients, however, the important thing to know when working with this method - you MUST have a starting point to discount from .. unless you want to have every single product with different prices based on a role which, if you have lots of products could cause you headaches to manage.

Use the Price Rules module for this.
Nina