Is it possible to add a piezo buzzer to a counter
Yes, just write your buzz() routine and call it on certain intervals of your count variable.  

If you want it to be every 10 counts, then do something like:

if((countD % 10) == 0) buzz(2, 2500, 500);

EDIT

The updated code won't work as intended. The % or "modulo"operator returns the remainder of division by the number. So e.g. 8 % 2 = 0 as 2 goes into 8 exactly. 8 % 3 = 2, as 2 only goes twice into 8 with remainder 2.
So you can see that the result can not be higher than the modulo value, so countD % 10 == 70 will never be true. If you want it to buzz on every 70th count as well, use if ((countD % 70) == 0) buzz(2, 6000, 500); - this will buzz on the 70th count, 140th count, 210th count and so on.  

If you need to specify every 10th count between certain values, then combine the mod with an and logic check like so:

if(((countD % 10) == 0)) &amp;&amp; ((countD &gt; 10) &amp;&amp; (countD &lt; 70))) buzz(2, 4000, 500);