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 $25.54   5.466%   $26.936   $26.94   $26.95   $26.90  
  Purchase #2 $43.71   3.161%   $45.0917   $45.09   $45.10   $45.10  
  Purchase #3 $239.41   9.336%   $261.7613   $261.76   $261.75   $261.80  
  Purchase #4 $240.50   5.411%   $253.5135   $253.51   $253.50   $253.50  
  Purchase #5 $103.43   10.459%   $114.2477   $114.25   $114.25   $114.20  
  Purchase #6 $155.53   5.140%   $163.5242   $163.52   $163.50   $163.50  
  Purchase #7 $80.47   3.355%   $83.1698   $83.17   $83.15   $83.20  
  7 purchase totals = $888.59       $948.2442   $948.24   $948.20   $948.20