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 $119.49   12.179%   $134.0427   $134.04   $134.05   $134.00  
  Purchase #2 $126.65   10.575%   $140.0432   $140.04   $140.05   $140.00  
  Purchase #3 $168.51   13.131%   $190.637   $190.64   $190.65   $190.60  
  Purchase #4 $164.87   3.261%   $170.2464   $170.25   $170.25   $170.20  
  Purchase #5 $12.92   11.172%   $14.3634   $14.36   $14.35   $14.40  
  Purchase #6 $237.73   7.617%   $255.8379   $255.84   $255.85   $255.80  
  Purchase #7 $132.74   4.770%   $139.0717   $139.07   $139.05   $139.10  
  7 purchase totals = $962.91       $1,044.2423   $1,044.24   $1,044.25   $1,044.10