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 $167.58   13.746%   $190.6155   $190.62   $190.60   $190.60  
  Purchase #2 $26.60   7.611%   $28.6245   $28.62   $28.60   $28.60  
  Purchase #3 $100.32   13.369%   $113.7318   $113.73   $113.75   $113.70  
  Purchase #4 $236.37   10.418%   $260.995   $261.00   $261.00   $261.00  
  Purchase #5 $19.52   13.704%   $22.195   $22.20   $22.20   $22.20  
  Purchase #6 $184.61   3.323%   $190.7446   $190.74   $190.75   $190.70  
  Purchase #7 $69.44   5.105%   $72.9849   $72.98   $73.00   $73.00  
  7 purchase totals = $804.44       $879.8913   $879.89   $879.90   $879.80