if a landlord in new jersey does not register his home as a rental, is there a fine?

There may be some local requirement for registration.  Call the Township offices and ask what the require of rentals.  Sometimes a specific Certificate of Occupancy, known as a CO is required.  If the landlord does not have that specific CO or has not fulfilled the registration requirements, they may face a local fine, or a restriction in their ability to rent.  Be careful, you may find yourself out of rental housing if the landlord cannot obtain the proper registration.