The human ear works really well...
(OK just going to edit this to add that I was definitely joking a bit. Sometimes the human ear is not accurate enough to account for music made with computers where the tempo is a result of abstracted systems upon systems and such or just really obfuscated artistic or structural intentions. Beyond that live performances can be genuinely challenging due to:
1.) Live tempo is almost never good-- especially when the band or group is entirely accoustic.
2.) Sometimes the recording can honestly just be fucked up and the speed is off.)
Honestly I don't think there is an analyzer that is perfect, because the program would have to be complex enough to understand what is a rhythmic beat (or representation of the time) and what is just noise.
This is why I suggest just listening, because, yes, sometimes the tempo is really precise, but in cases where a machine can't actually help you, a well trained ear can competently approximate the tempo AT least, and OSU! fortunately allows you to adjust the position of circles minutely to account for micro rhythms.