Tetrations and last digits

Let $a_0$ be any even integer larger than 0 but not divisible by 10.

And define $a_{n} = a_0^{a_{n-1}}$ for $n=1,2,3,\ldots$ .

For example, if $a_0 = 14$ , then $a_4 = 14^{14^{14^{14}}}$ .

Is it true that for any permissible initial value of $a_0$ , the last digit of $a_m$ is 6 for all integers $m\geq 3?$