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 $249.37   5.214%   $262.3722   $262.37   $262.35   $262.40  
  Purchase #2 $60.30   3.325%   $62.305   $62.31   $62.30   $62.30  
  Purchase #3 $48.32   4.318%   $50.4065   $50.41   $50.40   $50.40  
  Purchase #4 $13.74   3.804%   $14.2627   $14.26   $14.25   $14.30  
  Purchase #5 $35.81   8.149%   $38.7282   $38.73   $38.75   $38.70  
  Purchase #6 $141.75   10.868%   $157.1554   $157.16   $157.15   $157.20  
  Purchase #7 $25.59   6.175%   $27.1702   $27.17   $27.15   $27.20  
  7 purchase totals = $574.88       $612.4002   $612.41   $612.35   $612.50