To calculate \( f(-4) \) for the function \( f(x) = \left( \frac{x}{8} \right)^2 \), we first substitute \(-4\) for \(x\):
\[ f(-4) = \left( \frac{-4}{8} \right)^2 \]
Simplifying inside the parentheses:
\[ \frac{-4}{8} = -0.5 \]
Next, we square \(-0.5\):
\[ f(-4) = (-0.5)^2 = 0.25 \]
Now, rounding \(0.25\) to the nearest hundredth place, we simply get:
\[ 0.25 \]
Thus, the final answer is:
\[ \boxed{0.25} \]