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 $241.64   8.252%   $261.5801   $261.58   $261.60   $261.60  
  Purchase #2 $17.76   9.145%   $19.3842   $19.38   $19.40   $19.40  
  Purchase #3 $11.39   9.387%   $12.4592   $12.46   $12.45   $12.50  
  Purchase #4 $114.25   9.448%   $125.0443   $125.04   $125.05   $125.00  
  Purchase #5 $125.34   4.257%   $130.6757   $130.68   $130.70   $130.70  
  Purchase #6 $213.93   4.213%   $222.9429   $222.94   $222.95   $222.90  
  Purchase #7 $218.25   6.136%   $231.6418   $231.64   $231.65   $231.60  
  7 purchase totals = $942.56       $1,003.7282   $1,003.72   $1,003.80   $1,003.70