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 $224.62   6.516%   $239.2562   $239.26   $239.25   $239.30  
  Purchase #2 $204.27   5.193%   $214.8777   $214.88   $214.90   $214.90  
  Purchase #3 $230.40   3.367%   $238.1576   $238.16   $238.15   $238.20  
  Purchase #4 $159.78   3.552%   $165.4554   $165.46   $165.45   $165.50  
  Purchase #5 $246.76   6.482%   $262.755   $262.76   $262.75   $262.80  
  Purchase #6 $192.48   8.145%   $208.1575   $208.16   $208.15   $208.20  
  Purchase #7 $154.28   3.754%   $160.0717   $160.07   $160.05   $160.10  
  7 purchase totals = $1,412.59       $1,488.7311   $1,488.75   $1,488.70   $1,489.00