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 $239.95   9.113%   $261.8166   $261.82   $261.80   $261.80  
  Purchase #2 $42.99   9.362%   $47.0147   $47.01   $47.00   $47.00  
  Purchase #3 $52.63   8.659%   $57.1872   $57.19   $57.20   $57.20  
  Purchase #4 $176.87   13.602%   $200.9279   $200.93   $200.95   $200.90  
  Purchase #5 $183.37   6.489%   $195.2689   $195.27   $195.25   $195.30  
  Purchase #6 $34.64   7.605%   $37.2744   $37.27   $37.25   $37.30  
  Purchase #7 $49.92   6.849%   $53.339   $53.34   $53.35   $53.30  
  7 purchase totals = $780.37       $852.8287   $852.83   $852.80   $852.80