You don't need to transfer it unless the person buying it wants to. You can easily transfer ownership without transfering to a new registrar. If in fact the buyer wants to transfer to a new registrar then they would request the transfer, not you. Furthermore, you need to make sure the domain is unlocked and that you provide the buyer with the "domain secret" or transfer key. The administrative contact would have to approve the transfer.
Ep, glad to see you come back and tidy up...did want to ask a one day favor, I want to enhance my resume , was hoping you could make me administrator for a day, if so, take me right off since I won't be here to do anything, and don't know the slightest about the board, but it would be nice putting "served administrator osnn", if can do, THANKS