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 $93.98   4.370%   $98.0869   $98.09   $98.10   $98.10  
  Purchase #2 $68.33   3.491%   $70.7154   $70.72   $70.70   $70.70  
  Purchase #3 $109.46   4.599%   $114.4941   $114.49   $114.50   $114.50  
  Purchase #4 $107.81   10.620%   $119.2594   $119.26   $119.25   $119.30  
  Purchase #5 $58.69   5.797%   $62.0923   $62.09   $62.10   $62.10  
  Purchase #6 $217.45   6.556%   $231.706   $231.71   $231.70   $231.70  
  Purchase #7 $95.99   13.167%   $108.629   $108.63   $108.65   $108.60  
  7 purchase totals = $751.71       $804.9831   $804.99   $805.00   $805.00