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 $169.76   8.797%   $184.6938   $184.69   $184.70   $184.70  
  Purchase #2 $27.59   3.314%   $28.5043   $28.50   $28.50   $28.50  
  Purchase #3 $148.72   12.466%   $167.2594   $167.26   $167.25   $167.30  
  Purchase #4 $73.83   7.826%   $79.6079   $79.61   $79.60   $79.60  
  Purchase #5 $32.44   6.823%   $34.6534   $34.65   $34.65   $34.70  
  Purchase #6 $228.87   3.203%   $236.2007   $236.20   $236.20   $236.20  
  Purchase #7 $76.70   8.358%   $83.1106   $83.11   $83.10   $83.10  
  7 purchase totals = $757.91       $814.0301   $814.02   $814.00   $814.10