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 $239.30   5.588%   $252.6721   $252.67   $252.65   $252.70  
  Purchase #2 $97.37   8.235%   $105.3884   $105.39   $105.40   $105.40  
  Purchase #3 $124.56   12.838%   $140.551   $140.55   $140.55   $140.60  
  Purchase #4 $44.44   4.724%   $46.5393   $46.54   $46.55   $46.50  
  Purchase #5 $182.60   8.233%   $197.6335   $197.63   $197.65   $197.60  
  Purchase #6 $81.99   12.468%   $92.2125   $92.21   $92.20   $92.20  
  Purchase #7 $114.26   11.780%   $127.7198   $127.72   $127.70   $127.70  
  7 purchase totals = $884.52       $962.7166   $962.71   $962.70   $962.70