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 $215.84   8.724%   $234.6699   $234.67   $234.65   $234.70  
  Purchase #2 $168.57   12.389%   $189.4541   $189.45   $189.45   $189.50  
  Purchase #3 $23.94   7.497%   $25.7348   $25.73   $25.75   $25.70  
  Purchase #4 $52.63   5.242%   $55.3889   $55.39   $55.40   $55.40  
  Purchase #5 $94.54   10.602%   $104.5631   $104.56   $104.55   $104.60  
  Purchase #6 $25.34   5.541%   $26.7441   $26.74   $26.75   $26.70  
  Purchase #7 $151.33   4.368%   $157.9401   $157.94   $157.95   $157.90  
  7 purchase totals = $732.19       $794.4950   $794.48   $794.50   $794.50