Play it as it Lays
The firm rule at my game table is that rolls don’t count on the floor. Otherwise there’s the temptation to strategically count good rolls wherever they are while rerolling bad rolls. But, man does it suck when you get that natural 20 on the floor.
I’ve also seen a “only rolls on the book count” house rule used as well. While a little too firm for me, this does encourage rolling on a flat surface (i.e. a rulebook), preventing cocked dice. And it encourages the player to stop the roll, adding the extra randomization of a bounce. It’d probably be easier to just have dice trays.