\[- \left( - \frac{3}{5} \right)^{3} = \left( \frac{3}{5} \right)^{3} = \frac{3^{3}}{5^{3}} = \frac{3^{2} \cdot 3}{5^{2} \cdot 5} =\]
\[= \frac{9 \cdot 3}{25 \cdot 5} = \frac{27}{125}.\]