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 $8.46   13.797%   $9.6272   $9.63   $9.65   $9.60  
  Purchase #2 $224.77   5.402%   $236.9121   $236.91   $236.90   $236.90  
  Purchase #3 $192.30   11.301%   $214.0318   $214.03   $214.05   $214.00  
  Purchase #4 $40.74   6.138%   $43.2406   $43.24   $43.25   $43.20  
  Purchase #5 $178.68   10.179%   $196.8678   $196.87   $196.85   $196.90  
  Purchase #6 $186.78   5.301%   $196.6812   $196.68   $196.70   $196.70  
  Purchase #7 $65.68   6.138%   $69.7114   $69.71   $69.70   $69.70  
  7 purchase totals = $897.41       $967.0721   $967.07   $967.10   $967.00