The posted answers are absolutely correct that there is nothing that indicates one way or the other whether Luke buried his aunt and uncle. It's completely open to interpretation.
However, assuming he did not bury them, there is a simple explanation for why not: Shock.
This is a young man whose life has just been turned upside-down multiple times in a very short period of time, culminating in the death of the only parents he's ever known. He cannot possibly be thinking clearly. Quite possibly (even probably) the only thing he could think of to do was to return to the one parental figure he could think of: Obi-Wan. The idea of burying his aunt and uncle may not even have occurred to him, assuming that this was even an appropriate funeral practice for Tatooine.