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 $243.83   7.414%   $261.9076   $261.91   $261.90   $261.90  
  Purchase #2 $132.65   4.646%   $138.8129   $138.81   $138.80   $138.80  
  Purchase #3 $89.73   8.403%   $97.27   $97.27   $97.25   $97.30  
  Purchase #4 $59.63   11.142%   $66.274   $66.27   $66.25   $66.30  
  Purchase #5 $92.25   8.344%   $99.9473   $99.95   $99.95   $99.90  
  Purchase #6 $122.59   5.489%   $129.319   $129.32   $129.30   $129.30  
  Purchase #7 $216.78   11.321%   $241.3217   $241.32   $241.30   $241.30  
  7 purchase totals = $957.46       $1,034.8525   $1,034.85   $1,034.75   $1,034.80