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 $157.49   5.635%   $166.3646   $166.36   $166.35   $166.40  
  Purchase #2 $152.26   8.302%   $164.9006   $164.90   $164.90   $164.90  
  Purchase #3 $22.94   3.317%   $23.7009   $23.70   $23.70   $23.70  
  Purchase #4 $234.92   11.206%   $261.2451   $261.25   $261.25   $261.20  
  Purchase #5 $131.38   6.109%   $139.406   $139.41   $139.40   $139.40  
  Purchase #6 $148.42   8.305%   $160.7463   $160.75   $160.75   $160.70  
  Purchase #7 $91.64   9.580%   $100.4191   $100.42   $100.40   $100.40  
  7 purchase totals = $939.05       $1,016.7826   $1,016.79   $1,016.75   $1,016.70