Blade Tool Stuck on Grid in Final Cut
You can only cut in-between frames of your video clips.
Videos have generally frame rates per second of 24 or 25, maybe 30. Sound files have typically a sample rate per second of 48000. So you could say you can cut a video e.g. 25 times per second and a sound file 48000 times.
I usually cut to the nearest frame to the beat of the music. IMHO nobody can tell the difference of one or the other frame with a beat in between.
Try both versions and choose what feels the best.
FCPX is not sound editor like logic pro or pro tools. BPM don't apply for FCPX, it's the frame rate of the timeline and clips used what matters more.