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 $205.28   9.265%   $224.2992   $224.30   $224.30   $224.30  
  Purchase #2 $242.63   7.871%   $261.7274   $261.73   $261.75   $261.70  
  Purchase #3 $25.50   4.157%   $26.56   $26.56   $26.55   $26.60  
  Purchase #4 $107.53   11.836%   $120.2573   $120.26   $120.25   $120.30  
  Purchase #5 $101.69   10.786%   $112.6583   $112.66   $112.65   $112.70  
  Purchase #6 $246.57   3.750%   $255.8164   $255.82   $255.80   $255.80  
  Purchase #7 $35.27   9.451%   $38.6034   $38.60   $38.60   $38.60  
  7 purchase totals = $964.47       $1,039.9220   $1,039.93   $1,039.90   $1,040.00