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 $195.94   10.116%   $215.7613   $215.76   $215.75   $215.80  
  Purchase #2 $170.65   13.419%   $193.5495   $193.55   $193.55   $193.50  
  Purchase #3 $146.79   7.549%   $157.8712   $157.87   $157.85   $157.90  
  Purchase #4 $108.39   5.309%   $114.1444   $114.14   $114.15   $114.10  
  Purchase #5 $136.42   11.716%   $152.403   $152.40   $152.40   $152.40  
  Purchase #6 $115.45   8.439%   $125.1928   $125.19   $125.20   $125.20  
  Purchase #7 $193.79   6.563%   $206.5084   $206.51   $206.50   $206.50  
  7 purchase totals = $1,067.43       $1,165.4306   $1,165.42   $1,165.40   $1,165.40