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 $156.71   3.501%   $162.1964   $162.20   $162.20   $162.20  
  Purchase #2 $125.87   13.296%   $142.6057   $142.61   $142.60   $142.60  
  Purchase #3 $190.87   3.544%   $197.6344   $197.63   $197.65   $197.60  
  Purchase #4 $215.83   4.340%   $225.197   $225.20   $225.20   $225.20  
  Purchase #5 $246.38   13.605%   $279.9   $279.90   $279.90   $279.90  
  Purchase #6 $51.45   11.724%   $57.482   $57.48   $57.50   $57.50  
  Purchase #7 $153.38   10.336%   $169.2334   $169.23   $169.25   $169.20  
  7 purchase totals = $1,140.49       $1,234.2489   $1,234.25   $1,234.30   $1,234.20