If you're a carrier and filed IFTA with 1 km in PA then you will have created NEXUS in PA and you're obligated to fill out a tax return. Every state is different with their calculations of NEXUS but a lot of them still require a zero dollar tax return if you don't meet it and an explanation on how you calculated the value based on their NEXUS.
If you ignore the tax filings you will find out the hard way when a tractor linked to your USDOT gets stopped for any enforcement (scale, traffic ticket, accident investigation etc) and they hold it until the returns get filed and paid. It is not pleasant and takes a long time to sort out. They don't care about your equipment, the load or the driver because you are a foreign entity. Most new England states have increased enforcement and with the advent of everything getting computerized they have a much better visibility to all those carriers crossing their states through IFTA returns.
The following link shows what constitutes NEXUS in PA
Its been a long time since I have had to deal with this as I hired a US accountant to take care of all the states requiring returns. If my memory is correct PA is bases their NEXUS for carriers on the number pickups and deliveries in the state which is a taxable service. We meet the 'de-minimus' standard so we send a zero dollar return with the calculation showing we have very few deliveries/pickups in PA.