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 $103.54   12.557%   $116.5415   $116.54   $116.55   $116.50  
  Purchase #2 $15.36   8.203%   $16.62   $16.62   $16.60   $16.60  
  Purchase #3 $60.95   10.569%   $67.3918   $67.39   $67.40   $67.40  
  Purchase #4 $45.31   3.679%   $46.977   $46.98   $47.00   $47.00  
  Purchase #5 $213.88   13.504%   $242.7624   $242.76   $242.75   $242.80  
  Purchase #6 $214.92   13.607%   $244.1642   $244.16   $244.15   $244.20  
  Purchase #7 $209.88   9.345%   $229.4933   $229.49   $229.50   $229.50  
  7 purchase totals = $863.84       $963.9502   $963.94   $963.95   $964.00