When you're pulled over for a cop you're only required to roll the window down just enough to allow the passage of your drivers license as well as your vehicles registration and insurance card through.
You're not legally required to roll your window down all the way for a police officer.
However even if you leave your window rolled halfway up the police can still break your window out to get to you so it doesn't really make much difference.
However I just roll my window down a few inches because I don't trust cops and like a bit of protection between us.
Usually I find that most officers have no problem with passing the documents through the window that is halfway down.
I've had a few officers that tried to demand I roll it all the way down but I know the law and my rights.