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 $244.52   6.808%   $261.1669   $261.17   $261.15   $261.20  
  Purchase #2 $152.42   9.103%   $166.2948   $166.29   $166.30   $166.30  
  Purchase #3 $163.63   9.318%   $178.877   $178.88   $178.90   $178.90  
  Purchase #4 $122.61   8.111%   $132.5549   $132.55   $132.55   $132.60  
  Purchase #5 $95.28   8.593%   $103.4674   $103.47   $103.45   $103.50  
  Purchase #6 $83.67   12.680%   $94.2794   $94.28   $94.30   $94.30  
  Purchase #7 $18.71   8.311%   $20.265   $20.27   $20.25   $20.30  
  7 purchase totals = $880.84       $956.9054   $956.91   $956.90   $957.10