The penalties will cary depending on how you choose to handle the situation. If you know today that you do not wish to fulfill your contract, your penalties will likely be less if you contact your PD and give them fair warning to find another resident to fill your spot. Most will not penalize you for this action.
However, while legally your have fulfilled the match contract with NRMP by agreeing to sign a contract with your program, if you wait until July 1 and then back out, I am sure this will not be looked upon favorably. The NRMP can ban you from using their services for future matches and your PD may make it difficult for you to find another position, since most other programs will want a letter from your current PD in reference.