If you're playing it to your customers and you aren't paying for it then you are in trouble. Realistically though, your chances of being caught are slim.
Ever wonder why department stores play that awful muzak? That's why.
With one notable exception: stores which sell music are allowed to play the music they sell on their PA systems without royalties or permission. IIRC, the store does not have to sell only music or even primarily music, but they must sell enough of the music that they're playing to make a bona fide claim that they are playing the music to enhance sales of the music (rather than just sales in general).