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 $242.25   8.134%   $261.9546   $261.95   $261.95   $262.00  
  Purchase #2 $198.99   6.843%   $212.6069   $212.61   $212.60   $212.60  
  Purchase #3 $40.70   7.692%   $43.8306   $43.83   $43.85   $43.80  
  Purchase #4 $143.90   13.340%   $163.0963   $163.10   $163.10   $163.10  
  Purchase #5 $101.91   13.272%   $115.4355   $115.44   $115.45   $115.40  
  Purchase #6 $221.60   4.432%   $231.4213   $231.42   $231.40   $231.40  
  Purchase #7 $8.76   6.107%   $9.295   $9.30   $9.30   $9.30  
  7 purchase totals = $958.11       $1,037.6402   $1,037.65   $1,037.65   $1,037.60