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 $232.38   12.849%   $262.2385   $262.24   $262.25   $262.20  
  Purchase #2 $104.66   9.733%   $114.8466   $114.85   $114.85   $114.80  
  Purchase #3 $132.51   10.357%   $146.2341   $146.23   $146.25   $146.20  
  Purchase #4 $115.57   8.665%   $125.5841   $125.58   $125.60   $125.60  
  Purchase #5 $201.55   3.621%   $208.8481   $208.85   $208.85   $208.80  
  Purchase #6 $231.36   13.351%   $262.2489   $262.25   $262.25   $262.20  
  Purchase #7 $117.71   13.214%   $133.2642   $133.26   $133.25   $133.30  
  7 purchase totals = $1,135.74       $1,253.2645   $1,253.26   $1,253.30   $1,253.10