It depends. How much accuracy are you slotting in your attacks, and do you have any global accuracy bonuses? Both of those will have a very large effect on your tohit chances.
For what it's worth, the formula for your chance to hit is:
final CTH = (1 + accuracy) * (base tohit - defense + tohit buffs)
Base tohit varies depending on the level of your foe relative to you: for an even level foe it's 75%, for a +1 65%, for +2 56%, for +3 48%, for +4 39%, and for +5 30%.
So, for example, if you're fighting +3s with no defense and you have +6% tohit and a total of 60% accuracy between your slotting and accuracy bonuses, your final chance to hit is:
CTH = (1 + 0.6) * (0.48 - 0 + 0.06) = (1.6) * (0.54) = 0.864 = 86.4%
Is that enough? You have to decide. Personally I'm not satisfied until my tohit chance is above 90%. Take your build, figure out how much accuracy you have for each attack, calculate your final chance to hit against various levels of enemies with just the +6% tohit, and decide if you're happy with the results. If not, consider slotting more accuracy, looking for global accuracy bonuses in your sets, or taking tactical training: leadership for more +tohit. It all depends on how much accuracy you have slotted and just how purple you want to go.
@MuonNeutrino
Student, Gamer, Altaholic, and future Astronomer.
This is what it means to be a tank!
That was exactly what I wanted to know. Thank you very much 
My current build has a +6% chance to hit and I was wondering if that is enough? I enjoy soloing purples and I am afraid I should have picked up Tactical Maneuvers leadership instead of Assault.
So what is the magical +hit number I should be aiming for?