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 $24.29   7.193%   $26.0372   $26.04   $26.05   $26.00  
  Purchase #2 $51.38   8.277%   $55.6327   $55.63   $55.65   $55.60  
  Purchase #3 $163.89   4.864%   $171.8616   $171.86   $171.85   $171.90  
  Purchase #4 $68.77   11.831%   $76.9062   $76.91   $76.90   $76.90  
  Purchase #5 $28.55   5.724%   $30.1842   $30.18   $30.20   $30.20  
  Purchase #6 $95.66   4.567%   $100.0288   $100.03   $100.05   $100.00  
  Purchase #7 $157.69   9.639%   $172.8897   $172.89   $172.90   $172.90  
  7 purchase totals = $590.23       $633.5404   $633.54   $633.60   $633.50