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 $161.84   12.792%   $182.5426   $182.54   $182.55   $182.50  
  Purchase #2 $123.62   9.113%   $134.8855   $134.89   $134.90   $134.90  
  Purchase #3 $139.73   7.389%   $150.0546   $150.05   $150.05   $150.10  
  Purchase #4 $110.41   3.353%   $114.112   $114.11   $114.10   $114.10  
  Purchase #5 $25.61   4.408%   $26.7389   $26.74   $26.75   $26.70  
  Purchase #6 $119.48   3.537%   $123.706   $123.71   $123.70   $123.70  
  Purchase #7 $225.77   10.487%   $249.4465   $249.45   $249.45   $249.40  
  7 purchase totals = $906.46       $981.4861   $981.49   $981.50   $981.40