Ah, didn't realize the case was tapered. Yes, if the hole is tapered you want a countersunk screw. When you're mounting a flat surface, like the Pi to Helder's board from some of the photos I saw, you'll want a counterbore screw.
I hear that if you buy a $30 pack of screws from wermy, he will throw in a set of 3D printed parts for free! (sarcasm )
Edit: I don't want to provide bad advice but it looks like wermy's long screws are counterbore. I'll let the pros weigh in at this point.