How to deal with inequality signs when using a Z-table?

Question

Is there a significant difference (in results) between the $P(Z<s)$ and $P(Z\le s)$? The same goes with $>$ and $\ge$. My textbook uses all 4 of these symbols in the exercise questions, yet only uses $\le$ in the explanations (probably due to the fact that the Z-table gives you $P(Z\le z$ only). The answers at the back seem to indicate no difference between the presence and absence of the $=$ sign. Any help would be appreciated.