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 $103.73   10.659%   $114.7866   $114.79   $114.80   $114.80  
  Purchase #2 $43.57   3.149%   $44.942   $44.94   $44.95   $44.90  
  Purchase #3 $42.70   11.318%   $47.5328   $47.53   $47.55   $47.50  
  Purchase #4 $115.89   8.609%   $125.867   $125.87   $125.85   $125.90  
  Purchase #5 $12.30   13.134%   $13.9155   $13.92   $13.90   $13.90  
  Purchase #6 $91.87   5.617%   $97.0303   $97.03   $97.05   $97.00  
  Purchase #7 $242.66   13.753%   $276.033   $276.03   $276.05   $276.00  
  7 purchase totals = $652.72       $720.1072   $720.11   $720.15   $720.00