When I am trying to find my 1 RM or 5 RM maxes I make sure I go through a long warm up to get near the poundage I believe is my max. For example, if you think your 1RM bench press max is around 425 then go through a warmup like this:

Exercise Sets Reps Weight

*BP 2 5 45
2 3 95
1 3 135
1 3 185
1 3 225
1 3 275
1 1 315
1 1 365
1 1 405
1 1 425

It seems long but it helps your joints lubircated and enables your CNS to fire optimally. so you can put up the most weight. This is just an example that I use with my WSB training and have had good results with as I have to find my maxes every few weeks.

My main point is to warmup extensively so your body can handle the big weights but do it in such a way that you aren't draining your system. The only problem with adding a little weight at a time for 1 RM is that your doing alot of lifts over 90% of your maximum effort, which eventually puts a drain on your system and the muscles get fatigued. Try something where the increments are bigger so that your not doing alot of lifts that over 90% of your Max Effort for the lift. (This can be seen in the last two sets of the above warmup as the weight increases drop sharply near the max target.)

To your main question of finding a 5 Rep max, I haven't found a good warmup for them so I will give you an example of what I did. Here is an example warmup that was recommended to me when I was trying to find my 5 RM maxes for squats. So in this case the example warmup is for a 5 RM 225lb Squat:

Weight Reps Sets
45 x 5 x 2
95 x 5 x 2
135 x 5
185 x 5
225 x 5

Really you just have to find a good warmup routine that you feel gets you ready for the weight. The main thing I think is to have big enough weight increases so that your not doing to many lifts over 90% of your Maximum Effort. The above is just what works for me but it gives you a rough idea. Once you have found your 5 RM max the first time then you at least have something to compare your progress to the next time if you follow the same routine.