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 $98.47   5.242%   $103.6318   $103.63   $103.65   $103.60  
  Purchase #2 $226.25   10.830%   $250.7529   $250.75   $250.75   $250.80  
  Purchase #3 $47.98   3.447%   $49.6339   $49.63   $49.65   $49.60  
  Purchase #4 $240.50   8.863%   $261.8155   $261.82   $261.80   $261.80  
  Purchase #5 $157.83   7.166%   $169.1401   $169.14   $169.15   $169.10  
  Purchase #6 $124.38   12.131%   $139.4685   $139.47   $139.45   $139.50  
  Purchase #7 $187.52   4.785%   $196.4928   $196.49   $196.50   $196.50  
  7 purchase totals = $1,082.93       $1,170.9355   $1,170.93   $1,170.95   $1,170.90