Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $191.63   12.501%   $215.5857   $215.59   $215.60   $215.60  
  Purchase #2 $86.86   13.348%   $98.4541   $98.45   $98.45   $98.50  
  Purchase #3 $128.82   7.577%   $138.5807   $138.58   $138.60   $138.60  
  Purchase #4 $250.38   10.189%   $275.8912   $275.89   $275.90   $275.90  
  Purchase #5 $202.26   5.492%   $213.3681   $213.37   $213.35   $213.40  
  Purchase #6 $104.35   9.797%   $114.5732   $114.57   $114.55   $114.60  
  Purchase #7 $57.82   12.815%   $65.2296   $65.23   $65.25   $65.20  
  7 purchase totals = $1,022.12       $1,121.6826   $1,121.68   $1,121.70   $1,121.80