I would not advocate using this spelling of 'though.' I am a native speaker and have never used it. Not once.

If I am not mistaken it is just text lang for "though" placed at the end of a sentence. For example; "How do you like your pasta"? "Its alright but dat garlic bread tho"

Tho is an informal way of saying 'though' The meaning is exactly the same, so it is used as a conjunction or adverb: I got the job even though (tho) I failed the test. I enjoyed the movie, I'm not going again tomorrow, though (tho)