If it is a coincidental penalty, then the game remains 5 vs 5. Something like what antbogey just pointed out regarding 4 guys getting extra curricular penalties, most likely roughing, they will both get 2 minutes, and sit the same duration. There is to be no advantage or disadvantage, the game just plays as normal. The time they sit is more of a personal punishment, then punishing the team in anyway.

Assuming minor penalties, if there is more than just one penalty to each team or if one team already is playing short handed, then they just cancel. So for the TB/ATL game, there were 4 penalties, 2 to each team, so they cancel 5 on 5. If it were just two guys, 1 from each team, then 4 on 4. Anytime there are two majors you cancel.

On an aside the really fun one is when there is a major with the other team getting a minor in the last 5 minutes of a game. Then I believe the extra 3 minutes is played first instead of 4 on 4 for 2 minutes and then 5 on 4 the remaining three, it’s 5 on 4 for 3 minutes.

Anyways, here is the link to the coincidental penalty rule 19.1

http://www.nhl.com/ice/page.htm?id=26299

and here is their table for when there are lots of crazy penalties and they are canceled.

http://www.nhl.com/ice/page.htm?id=26556

This is a lot more complicated than I thought… Even after I get done fully digesting this, my wife won’t care to listen to all this minutae. But I do! Thanks Kev!