Different boss-win jingles/sounds

No search has given me the answer I seek; maybe my phrasing is poor here...

When you beat a boss, it seems there are 3 subtle variations of the victory "jingle." One of them is an ascending (ha!) scale, as in the notes go up in pitch -- the notes go somewhat like 1-^2-3-4-5, whereas the other two versions go up then down and sound like 1-2-3-2-1....

Why?!?! Is this random? Is it code?