NJ specifically does not allow windshield or front (driver and front seat passenger) windows to be tinted. Any other windows are allowed to be tinted. Minimum VLT is 5%.
Speaking from experience, if you have a high % on your front window (not windshield) you typically will not have any issues. 35%, 50%, and 70% offer some protection without making you a target, as they are relatively easy to see through even at night time. I've had 5 of my vehicles tinted, and I drive roughly 25,000 miles a year, No issues so far. I'm also 25 car enthusiast, so i'm typically seen as a moving $ for smaller townships. Nothing against the police, I just get followed a lot.
In the rare event you get stopped, it is a $54 ticket. No points. Obviously better not to get one at all, but all in all the likelihood you'll get stopped is slim to none unless your doing something really wrong.
Here are some links as references
http://www.state.nj.us/mvcbiz/pdf/Business_Licenses/Sunscreening%20Regs.pdf
https://www.windowtint.com/pages/new-jersey
http://tintlaws.com/new-jersey-window-tint-law.php
http://www.nj.com/traffic/index.ssf/2015/12/how_many_tickets_are_issued_for_tinted_windows_ask.html
