The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.4642\\[1 em]x_2 &= -0.2321+0.402i\\[1 em]x_3 &= -0.2321-0.402i \end{aligned} $$Step 1:
Get rid of fractions by multipling equation by $ \color{blue}{ 10 } $.
$$ \begin{aligned} -x^3+\frac{1}{10} & = 0 ~~~ / \cdot \color{blue}{ 10 } \\[1 em] -10x^3+1 & = 0 \end{aligned} $$Step 2:
Polynomial $ -10x^3+1 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.