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 $239.73   11.136%   $266.4263   $266.43   $266.45   $266.40  
  Purchase #2 $124.71   6.849%   $133.2514   $133.25   $133.25   $133.30  
  Purchase #3 $73.74   3.275%   $76.155   $76.16   $76.15   $76.20  
  Purchase #4 $78.29   10.305%   $86.3578   $86.36   $86.35   $86.40  
  Purchase #5 $32.53   10.591%   $35.9753   $35.98   $36.00   $36.00  
  Purchase #6 $32.50   5.420%   $34.2615   $34.26   $34.25   $34.30  
  Purchase #7 $137.64   4.211%   $143.436   $143.44   $143.45   $143.40  
  7 purchase totals = $719.14       $775.8633   $775.88   $775.90   $776.00