Yes. Go to the results tab and then find "pick winners" on the left-side navigation.
Winners are not notified so you can pick any of the contestants as a winner and let them know yourself. Just keep in mind that the leaderboard is public and the rankings are listed there for everyone to see so it's best to choose your winners very carefully based on that.
The winner picking tool only uses our random entry generator to pick the winners (up to 20 max).