For heavy squats, I'll rest anywhere between 3- 5minutes, depending on how I feel. but I"m also a big fan of supersetting to keep my heart rate up, it keeps me leaner year round, so in between squat sets I'll pick something light, like pushups, and do a quick set in between.
For me the key is making sure I can get all the reps on all the sets, I've always found that if I get all 5x5, then when I add my 5 or 10lbs, it's a guarantee that I'll get at least 3 sets of 5 on the increase the next workout, if not all 5. Sticking to this also keeps my form clean as I'm not trying to go too heavy.