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 $237.96   7.275%   $255.2716   $255.27   $255.25   $255.30  
  Purchase #2 $114.99   8.189%   $124.4065   $124.41   $124.40   $124.40  
  Purchase #3 $70.55   8.452%   $76.5129   $76.51   $76.50   $76.50  
  Purchase #4 $210.74   11.200%   $234.3429   $234.34   $234.35   $234.30  
  Purchase #5 $199.25   7.364%   $213.9228   $213.92   $213.90   $213.90  
  Purchase #6 $98.83   7.821%   $106.5595   $106.56   $106.55   $106.60  
  Purchase #7 $22.75   9.722%   $24.9618   $24.96   $24.95   $25.00  
  7 purchase totals = $955.07       $1,035.9780   $1,035.97   $1,035.90   $1,036.00