I do .4$ for HJ, and more if there is some other extras--most often, .6$ if a BJ; .8$ up to $ if FS. Tips can be a little more or less depending on other factors, such as how good the massage is and the number and quality of the extras.
Sometimes, if the session is great, I ask for more time and pay proportionately more both on the tip and the base fee for the extra time. So, for example, even if there is only one HJ, I might pay .6$ tip for the HJ in a 90-minute session.
Only one girl ever tried to charge me more for doing the same extra twice in the same session, such as two HJ--and so I never went back to see her again. In fact, I almost never go back to a girl who asks for any particular tip or for an increased fee. In a new place, I usually pay the fee in advance and the tip at the end. In repeat places, I usually pay both the fee and the tip at the end. Whatever I hand over at the end, her best reaction (in terms of my deciding to come back again) would be to pocket it thankfully without looking to see how much it was until after I'm gone.