Actually you don't even have to tag the mob.

As long as you start the event, someone else can tag it and receive loot rights for their party/group.
When it dies, its yours as far as quest completion goes.

See if you can dps or heal for another group and have them tank for your team.
You can provide a lot of whatever they're missing, and not having to focus on all of dps/heals/tanking at once, makes it a lot easier on you.