Density $\rho = \text{mass}/\text{volume}$. The relative error in density is $\frac{\Delta \rho}{\rho} = \frac{\Delta m}{m} + \frac{\Delta V}{V}$. Plugging in the values: $\frac{\Delta \rho}{\rho} = \frac{0.05}{5.00} + \frac{0.05}{1.00} = 0.01 + 0.05 = 0.06$. Multiplying by $100$ to get the percentage error gives $6\%$. This represents the maximum possible uncertainty in the density value.