But what kind of ending? If it's a simple 1 root chord on beat 1 of the last bar of the song, just add it. If it's a ritardando, the tempo is handled by the DAW.
My point is, song endings are song specific, in my opinion. Endings can be easily added to fit the song much better than 'canned' endings could ever fit.
But again, I don't know exactly what you have in mind regarding endings.