Most people don't actually sit and calculate the tip they leave to the nearest penny, but it's nice to be able to do this if you want to make sure that you leave an appropriate tip.
Here's an example of how to figure out your tip EXACTLY:
Let's say that you want to leave a 15% tip. BILL: $44.77 METHOD: 44.77 x .15 --------- 22385 4477 --------- 6.7155 ROUNDED TO NEAREST PENNY: $6.72