I have this macro in IsBoxer that I use for my dungeon team. It is run in step 1 of my dps key and sent to all others.

/stopmacro [@target, nodead, exists, harm]
/assist {SLOT1}
SLOT1 being my tank. This lets my tank switch targets rounding mobs up while my DPS just stays on one until its dead. I have a separate assist key on my mouse to have them switch targets if needed.

For a full DPS team you could use {FTL} instead of {SLOT1}