title: rounding a number in input but keep full decimal value in model
body: <p>I hope that title made sense. Basically I have an small app that does various social security calculations. A user can enter information like birth date, gender, salary etc, and click "calculate social security" and their monthly social security payouts display in an input field. The user can also, if they choose, enter that number in manually. The problem is that the value for that calculation is used elsewhere in the app, so for accuracy, i think I need the full decimal value. But cosmetically, i only need it to the dollar value (2046 vs 2046.3339228485938 bla bla bla). I've seen several tutorials on writing directives for that but that will change the value in the model.  It's crossed my mind that i may be going about this the wrong way entirely but i'm turning to stackoverflow in the hopes that this is a common issue that I just cant seem to find the right words for to google.</p>
  
  <p>thanks,
  John</p>