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 $66.25   13.497%   $75.1918   $75.19   $75.20   $75.20  
  Purchase #2 $167.97   5.281%   $176.8405   $176.84   $176.85   $176.80  
  Purchase #3 $106.71   7.282%   $114.4806   $114.48   $114.50   $114.50  
  Purchase #4 $100.89   4.828%   $105.761   $105.76   $105.75   $105.80  
  Purchase #5 $249.97   4.436%   $261.0587   $261.06   $261.05   $261.10  
  Purchase #6 $214.38   8.330%   $232.2379   $232.24   $232.25   $232.20  
  Purchase #7 $19.49   9.196%   $21.2823   $21.28   $21.30   $21.30  
  7 purchase totals = $925.66       $986.8528   $986.85   $986.90   $986.90