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 $242.67   4.688%   $254.0464   $254.05   $254.05   $254.00  
  Purchase #2 $47.50   5.854%   $50.2807   $50.28   $50.30   $50.30  
  Purchase #3 $82.58   10.179%   $90.9858   $90.99   $91.00   $91.00  
  Purchase #4 $46.28   10.428%   $51.1061   $51.11   $51.10   $51.10  
  Purchase #5 $55.71   4.231%   $58.0671   $58.07   $58.05   $58.10  
  Purchase #6 $102.48   11.713%   $114.4835   $114.48   $114.50   $114.50  
  Purchase #7 $209.74   10.734%   $232.2535   $232.25   $232.25   $232.30  
  7 purchase totals = $786.96       $851.2231   $851.23   $851.25   $851.30