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 $49.80   13.719%   $56.6321   $56.63   $56.65   $56.60  
  Purchase #2 $56.89   6.679%   $60.6897   $60.69   $60.70   $60.70  
  Purchase #3 $112.86   3.867%   $117.2243   $117.22   $117.20   $117.20  
  Purchase #4 $58.43   4.660%   $61.1528   $61.15   $61.15   $61.20  
  Purchase #5 $240.63   8.647%   $261.4373   $261.44   $261.45   $261.40  
  Purchase #6 $28.49   3.190%   $29.3988   $29.40   $29.40   $29.40  
  Purchase #7 $213.94   10.398%   $236.1855   $236.19   $236.20   $236.20  
  7 purchase totals = $761.04       $822.7205   $822.72   $822.75   $822.70