I try to keep 10 ea in stock .15mm to .5mm (.05mm increments) 5 ea in stock .55 to 1.0mm, and 3 in stock up to 3mm.
Starting at 2mm I only go for .1mm increments.
Bear in mind the used ones are plenty sharp, but the smaller sizes they sell are almost always bent ever so slightly. Perfectly fine for hand drilling, not so fine if you are using them in a drill press...