Since Ed Johnson is not available I will give an answer.
References are to Publication 463 (2007), Travel, Entertainment, Gift, and Car Expenses
When Tax Home is discussed in that publication it says, in part:
Generally, your tax home is your regular place of business or post of duty, regardless of where you maintain your family home. It includes the entire city or general area in which your business or work is located.
If you do not have a regular or a main place of business because of the nature of your work, then your tax home may be the place where you regularly live.
This is the area that has resulted in varied advice. That is, where is your main place of business or do you not have a main place of business ?
Since you work for the same employer in New Jersey that would certainly be your main place of business if you always worked in one location in New Jersey. In that case you would not deduct any expenses for travel from PA to NJ or NJ to PA.
Your case is not so clear as you work in various places in NJ for that one employer.
Case 1: IF most of those places you work in NJ are in the same metropolitan area it would still be your main place of business. In that case, you would deduct travel to and from any job locations that are not part of the main metropolitan area that you worked in. Still you would not deduct any expenses for travel from PA to NJ or NJ to PA.
Case 2: IF most of those places you work in NJ are NOT in the same metropolitan area it would not be your main place of business. The rules for no main place of business would apply. In that case, you would deduct travel to and from any job locations that are away form your tax home. There are three factors to consider where your tax home is when you do not have a main place of business.
Factors used to determine tax home. If you do not have a regular or main place of business or work, use the following three factors to determine where your tax home is.
You perform part of your business in the area of your main home and use that home for lodging while doing business in the area.
You have living expenses at your main home that you duplicate because your business requires you to be away from that home.
You have not abandoned the area in which both your historical place of lodging and your claimed main home are located; you have a member or members of your family living at your main home; or you often use that home for lodging.
If you satisfy all three factors, your tax home is the home where you regularly live. If you satisfy only two factors, you may have a tax home depending on all the facts and circumstances. If you satisfy only one factor, you are an itinerant; your tax home is wherever you work and you cannot deduct travel expenses.
Using those factors it would appear that your tax home is PA. In that case you would deduct expenses for travel from PA to and from NJ or in NJ from job to job.
The key fact to decide is if you work enough in one metropolitan area of NJ for that to be your main place of business (See Case 1) OR if your locations in NJ during the year are not mainly in one metropolitan area of NJ (See Case 2).
It does seem possible that the key fact may be decided differently from year to year. For example, one year you may have several assignments all in one metropolitan area so that area wold be your main place of business for that year and only deduct as in Case 1; but in the next year when you have many shorter and more distant assignments you do not have a main metropolitan area in which you work and you deduct as in Case 2.
Of course, your work and life do not fit so neatly around the calendar year and a year by year decision may not be best truly reflect the facts in your case. That is, when viewed in the longer term it is clear that over the many years you have worked in NJ it has been in one area (Case 1) or it has not been mainly in one metroplitan area (Case 2) so that case is how you will report it every year (even when there is a year that does not fit the overall long term pattern).
What you need to do is keep very good records of the amounts and locations of your travel expenses and apply the rules for deciding the key factor in the manner that best fits your situation.
I hope this answer, though a bit long, helps you to see the rules to apply and gives you a basis to make that decision.
Please ask if you need clarification.