In most cases lots of people put stops at even numbers. In this case we assume its $40 were lots of stops hang out. If you are in at 40 with many other players and you get stopped out the wave of selling that is triggered by the stop loss coulld give you a bad execution maybe you will be flushed to 39.90. If you put your stop 1 or 2 cents ahead it will be your stop that triggers the wave of stops at 40 and your exectution will be at a better price. Adding to this that putting stops at logical support resistance lines is not smart anyway as stop hunt algo's try to trigger these levels. In this case the stop price is a couple of bucks away but on shorter time frames I like to put a stop @ 2*ATR from my entry price.