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 $51.80   9.143%   $56.5361   $56.54   $56.55   $56.50  
  Purchase #2 $223.97   11.408%   $249.5205   $249.52   $249.50   $249.50  
  Purchase #3 $125.83   8.798%   $136.9005   $136.90   $136.90   $136.90  
  Purchase #4 $222.43   10.311%   $245.3648   $245.36   $245.35   $245.40  
  Purchase #5 $8.32   11.503%   $9.277   $9.28   $9.30   $9.30  
  Purchase #6 $21.56   6.225%   $22.9021   $22.90   $22.90   $22.90  
  Purchase #7 $241.30   8.466%   $261.7285   $261.73   $261.75   $261.70  
  7 purchase totals = $895.21       $982.2295   $982.23   $982.25   $982.20