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 $246.95   8.773%   $268.6149   $268.61   $268.60   $268.60  
  Purchase #2 $57.38   12.610%   $64.6156   $64.62   $64.60   $64.60  
  Purchase #3 $226.59   9.639%   $248.431   $248.43   $248.45   $248.40  
  Purchase #4 $139.73   8.485%   $151.5861   $151.59   $151.60   $151.60  
  Purchase #5 $11.97   6.316%   $12.726   $12.73   $12.75   $12.70  
  Purchase #6 $32.69   9.379%   $35.756   $35.76   $35.75   $35.80  
  Purchase #7 $44.65   13.498%   $50.6769   $50.68   $50.70   $50.70  
  7 purchase totals = $759.96       $832.4065   $832.42   $832.45   $832.40