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 $242.74   9.593%   $266.026   $266.03   $266.05   $266.00  
  Purchase #2 $73.50   4.442%   $76.7649   $76.76   $76.75   $76.80  
  Purchase #3 $71.25   9.866%   $78.2795   $78.28   $78.30   $78.30  
  Purchase #4 $87.34   6.414%   $92.942   $92.94   $92.95   $92.90  
  Purchase #5 $244.66   6.778%   $261.2431   $261.24   $261.25   $261.20  
  Purchase #6 $228.31   8.630%   $248.0132   $248.01   $248.00   $248.00  
  Purchase #7 $23.59   10.745%   $26.1247   $26.12   $26.10   $26.10  
  7 purchase totals = $971.39       $1,049.3934   $1,049.38   $1,049.40   $1,049.30