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 $139.58   12.522%   $157.0582   $157.06   $157.05   $157.10  
  Purchase #2 $241.96   12.223%   $271.5348   $271.53   $271.55   $271.50  
  Purchase #3 $148.66   7.553%   $159.8883   $159.89   $159.90   $159.90  
  Purchase #4 $42.60   9.385%   $46.598   $46.60   $46.60   $46.60  
  Purchase #5 $215.42   4.433%   $224.9696   $224.97   $224.95   $225.00  
  Purchase #6 $169.50   11.154%   $188.406   $188.41   $188.40   $188.40  
  Purchase #7 $217.49   7.694%   $234.2237   $234.22   $234.20   $234.20  
  7 purchase totals = $1,175.21       $1,282.6786   $1,282.68   $1,282.65   $1,282.70