SD under different tax assumptions

I am just throwing out this out here as I am not very clear on this. If one calculates the expected return and SD for a portfolio using a simulation tool, should you expect different standard deviation under different tax assumptions for the same portfolio. Reasoning – part of the volatility in the returns is shared by the tax office. Or it is not that material and one could apply the tax rate on top of the simulated results. I am asking this question as the package I am using at the moment is not able to utilise tax assumptions when simulating results and applies the tax rate on the ER after it has calculated the results.