To simplify \((5^4)^6\) using the Power Rule of Exponents, you multiply the exponents. The Power Rule states that \((a^m)^n = a^{m \cdot n}\).
So, applying this rule:
\[ (5^4)^6 = 5^{4 \cdot 6} = 5^{24} \]
Thus, the simplified expression is \(\boxed{5^{24}}\).