I used to put 5% and sometimes 20% on all of my cars before. If I got pulled over for something else they'd always tack on the tint tickets. This was back in NY. The back doors and rear window could be painted black for all they cared. But the front doors couldn't be below 35% and on the windshield you could only tint from the top down to the arrows. Just enough for a banner type tint.
One other thing, especially concerning nervous cops. If you get pulled over you better get that window down before the cop comes up to your window. I have had guns pulled on me cause he couldn't see what I was doing in the car. I can't blame them though. I'd be pretty nervous also.
I don't have any on my SVT now cause I'd want it uniform all around. and out here in Calif you can only have it so dark on the front doors.