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 $182.36   13.104%   $206.2565   $206.26   $206.25   $206.30  
  Purchase #2 $116.36   5.388%   $122.6295   $122.63   $122.65   $122.60  
  Purchase #3 $125.67   8.426%   $136.259   $136.26   $136.25   $136.30  
  Purchase #4 $18.41   3.338%   $19.0245   $19.02   $19.00   $19.00  
  Purchase #5 $149.92   7.599%   $161.3124   $161.31   $161.30   $161.30  
  Purchase #6 $136.66   4.106%   $142.2713   $142.27   $142.25   $142.30  
  Purchase #7 $105.69   9.463%   $115.6914   $115.69   $115.70   $115.70  
  7 purchase totals = $835.07       $903.4446   $903.44   $903.40   $903.50