In case of a tie, the President would get chosen by the House of Representatives, and the Vice-President by the Senate. (See the Constitution, particularly Article II, Section 1, and Amendment XII.) Normally we don't worry about this -- out of 500+ electoral votes, a tie seems unlikely. But the last election swung on a single state with 20-some votes, and they are talking about some 7-vote states as being key this time. It doesn't seem that hard to wind up with a tie.
So there certainly is an argument for treating one's Congressional votes as essentially "backup" for the Presidential one. It's still not *too* likely to become an issue, but it's another consideration for the stew...