Money" is the one with the cash register.

Yes — that’s “Money” from Pink Floyd’s The Dark Side of the Moon.

The song opens with a tape loop of a cash register clanking, coins dropping, and a telephone ringing. They built it by splicing together actual sound effects into a 7-beat loop, then used that loop as the rhythmic backbone for the whole track. It’s one of the most recognizable song intros in rock history.

That loop is also why the song feels slightly off-kilter — it’s in 7/4 time, which makes the cash register rhythm stumble in a way that fits perfectly.