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 $82.52   13.595%   $93.7386   $93.74   $93.75   $93.70  
  Purchase #2 $218.60   9.563%   $239.5047   $239.50   $239.50   $239.50  
  Purchase #3 $232.56   12.536%   $261.7137   $261.71   $261.70   $261.70  
  Purchase #4 $30.83   4.458%   $32.2044   $32.20   $32.20   $32.20  
  Purchase #5 $70.30   5.803%   $74.3795   $74.38   $74.40   $74.40  
  Purchase #6 $70.52   5.599%   $74.4684   $74.47   $74.45   $74.50  
  Purchase #7 $227.65   4.237%   $237.2955   $237.30   $237.30   $237.30  
  7 purchase totals = $932.98       $1,013.3048   $1,013.30   $1,013.30   $1,013.30