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 $240.81   11.574%   $268.6813   $268.68   $268.70   $268.70  
  Purchase #2 $204.71   6.429%   $217.8708   $217.87   $217.85   $217.90  
  Purchase #3 $69.26   6.638%   $73.8575   $73.86   $73.85   $73.90  
  Purchase #4 $113.65   10.574%   $125.6674   $125.67   $125.65   $125.70  
  Purchase #5 $27.48   11.679%   $30.6894   $30.69   $30.70   $30.70  
  Purchase #6 $70.39   11.482%   $78.4722   $78.47   $78.45   $78.50  
  Purchase #7 $216.78   10.361%   $239.2406   $239.24   $239.25   $239.20  
  7 purchase totals = $943.08       $1,034.4792   $1,034.48   $1,034.45   $1,034.60