Yes I do realize that they are the official nominees but I'm not forced to vote. I doubt the election is going to be decided by one measly vote.
Depending on your state your vote means less, even then every vote does have a statistical value to it. For example, you don't like trump or hillary then vote independent and raise their turnout rate to 15% so they have a chance of actually winning in the future, maybe if bernie ran as one in 2020.
Not voting at all just means you're letting other people make decisions for you.