the quantizing function is on the menu in the pianoroll...
Right-click the little piano (#1 on the pic)
Tools/Quick Quantize or
Tools/Quantize
what you do with it is up to you... Sometimes, you need quantize... sometimes, it fu*ks the groove you wanted to give in the 1st place...
There is a whole lot of other tools you got there too, so have fun with it...