Name of this movie: desert setting, guy holds hostages at store, black guy sings and makes everybody sing?

The part I remember seeing was where a black hostage wanted an old guy to play something different on the harmonica. So black guy starts singing over old guy and makes most eveybody around start to sing too o.o The cops around the building seem to follow some script. Black guy gets tired of heat, so him and Hispanic guy ask cops for tickets to mexico... >.>