Keeping in mind that your organization's by-laws will trump Robert's Rules, you can find quickly find information about the President and voting in Robert's Rules of Order, 10th edition by looking in the index under "President". The portions most likely to be applicable to your question are:

can vote to make or break a tie, pages 392-393
duties of, pages 332, 433-436
makes motions and votes on small boards, page 471
vote of, page 400

I am new to our PTO board for the upcoming year, someone has stated that the president of the board does not vote in an election of an incoming board/or at all. Where in Roberts Rule's can I find this with out reading the whole thing.