AmTote D&D5E Forgotten Realms
Preferably, dice rolls should be done with physical dice, though if you like digital I will allow them provided they come from a reputable source (read: not weighted)
Die rolls that fall off the rolling surface must be re-rolled.
I will typically make my die rolls behind the DM screen, primarily because I will be doing a lot of it, and rolling the die in the open can break player immersion ("Why did he just roll? It was really high… Is he rolling a monster's sneak check against us?…")
I also may not share difficulty checks (DC) if your in-game character would not reasonably be able to determine how difficult a task is. For example, it is likely that one could judge how hard it would be to push a rock down a hill with a Strength check, however it would not be clear how hard it would be to notice a secret door with Perception.