I am sure it has happened, but the chances are probably in the millions to one. Your more likely to get in a car accident on the way to the bank, then finding a silver dime in a penny box.
I started tossing dimes found in cent rolls aside until I had enough to go to my local coin shop and buy some junk mercs, so I guess in a way it's like finding silver in pennies.
Yes, I also found a silver dime in a roll of cents, a definite surprise for sure. It does happen. Just this past weekend while searching a box of dimes, of which most of the rolls had shinny new 2017 dimes, in the middle of all the shine was a white rim silver dime.
It wasn't my box, but a couple months ago, my friend Dustin (the bank teller) brought over a wheat penny collection dump for us to look through. We actually found a 1898 Barber dime in one of the rolls, so that was pretty incredible!