Very hard to hold aggro of 5 mobs shooting from afar. No tank can seriously be at 5 places at the same time!
but like someone said above, you just need to hold aggro of the strongest one.
A good healer will easily heal up everyone at the same time if everyone else are doing their job right and the tank will be ok.
Im sorry but thats a terrible approach. In game im a sith sorc heal spec. Ive run plenty of PUGS with terrible tanks who think they only have to solo attk one target and i end up having one mob on them and three mobs on me.
If you tank it is your job to grab all the targets. At least start with one and and chain that melee to a ranged then to another ranged mob.
Its like people dont have the slightest clue about healing aggro and stand there tanking one mob fight after fight while the cloth wearing healer actually takes all the damage. You can "get away" with it on trash pulls but ive had tanks do the same thing on boss pulls. That 4 mini boss pull on Mand Raiders with a bad tank and your approach Pfft.
You do your job i do mine. Dont make me do both thats just lazy, and crap ...