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 $239.68   10.387%   $264.5756   $264.58   $264.60   $264.60  
  Purchase #2 $109.91   4.334%   $114.6735   $114.67   $114.65   $114.70  
  Purchase #3 $44.65   5.492%   $47.1022   $47.10   $47.10   $47.10  
  Purchase #4 $81.54   13.763%   $92.7624   $92.76   $92.75   $92.80  
  Purchase #5 $164.65   5.797%   $174.1948   $174.19   $174.20   $174.20  
  Purchase #6 $121.92   11.522%   $135.9676   $135.97   $135.95   $136.00  
  Purchase #7 $64.33   13.411%   $72.9573   $72.96   $72.95   $73.00  
  7 purchase totals = $826.68       $902.2334   $902.23   $902.20   $902.40