Which of the following values is the greatest?

Let's convert all options into simple decimal form to compare them easily:
* Option A: $\sqrt{0.09}=0.3$
* Option B: $\sqrt[3]{0.064}=0.4$
* Option C: $\frac{3}{5}=0.6$
* Option D: $0.5$

Comparing the values: $0.6>0.5>0.4>0.3$. Therefore, $\frac{3}{5}$ is the greatest.