Depending on the type of campaign I'm running, I'll occasionally choose to roll out in the open. I also roll in the open with physical dice when it could lead to something major.
I always roll behind the screen. Actually, I've got a dice rolling app I use that lets me keep track of multiple modifiers for large groups of monsters without having to do the math every single time. It also keeps track of the last 20 rolls, so if there is any question about me fudging, I can...