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 $49.63   12.259%   $55.7141   $55.71   $55.70   $55.70  
  Purchase #2 $192.41   3.742%   $199.61   $199.61   $199.60   $199.60  
  Purchase #3 $34.30   9.279%   $37.4827   $37.48   $37.50   $37.50  
  Purchase #4 $98.87   4.361%   $103.1817   $103.18   $103.20   $103.20  
  Purchase #5 $26.99   12.511%   $30.3667   $30.37   $30.35   $30.40  
  Purchase #6 $73.60   3.870%   $76.4483   $76.45   $76.45   $76.40  
  Purchase #7 $28.63   7.190%   $30.6885   $30.69   $30.70   $30.70  
  7 purchase totals = $504.43       $533.4920   $533.49   $533.50   $533.50