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 $141.87   11.131%   $157.6615   $157.66   $157.65   $157.70  
  Purchase #2 $248.89   5.176%   $261.7725   $261.77   $261.75   $261.80  
  Purchase #3 $202.32   4.361%   $211.1432   $211.14   $211.15   $211.10  
  Purchase #4 $177.34   11.362%   $197.4894   $197.49   $197.50   $197.50  
  Purchase #5 $43.82   9.508%   $47.9864   $47.99   $48.00   $48.00  
  Purchase #6 $182.78   8.225%   $197.8137   $197.81   $197.80   $197.80  
  Purchase #7 $208.99   4.281%   $217.9369   $217.94   $217.95   $217.90  
  7 purchase totals = $1,206.01       $1,291.8036   $1,291.80   $1,291.80   $1,291.80