Why would you want to pay to NJ the amount of out-of-state sales paid to other states BASED ON YOUR INCOME since you didn't pay to NJ when you bought the items? IE, you bought something on-line and the seller didn't collect NJ sales tax because the seller had no nexus to NJ.

As a good taxpayer and CPA, when I bought stuff from Amazonia online and BEFORE they collected NJ sales tax by opening several warehouse in NJ, therefore charging me zero sales tax, I put the amount I owed on line 51. (I bought labels online in 2012, and charged myself $3.88 which I included on my 1040.)

Why not use actual, unless you have tens of thousands of dollars of purchases?