5^an constant mod 100000?

\[ \begin{array} { l c c }
25 ^ 1 & \equiv 25 & \pmod{1000} \\ 25 ^ 2 & \equiv 625 & \pmod{1000} \\ 25 ^ 3 & \equiv 625 & \pmod{1000} \\ 25 ^ 4 & \equiv 625 & \pmod{1000} \\ \vdots & \vdots & \vdots \\ \end{array} \]

We know that the last 3 digits of \( 25 ^ n \) will always be a constant 625 for large enough integer values of \( n \).

What is the smallest positive integer value \(a\) such that the last 5 digits of \( \left( 5 ^ a \right) ^n \) will always be a constant for large enough integer values of \( n \)?

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