If you are a good worker (Show up on time, work hard, put in extra effort, etc.) then ask.

But ask with the evidence that you deserve a raise based on your merit and your work ethic, not becasue your employer got a tax cut.

The tax cut will not be fully realized for a few years. The market will work this out but we don't know exactly what will happen. Maybe prices will go down, maybe more people will be hired, maybe everyone will get a raise, who knows exactly how it will work itself out.

But asking for a raise based solely on the fact that the company you work for got a tax cut, and the fact that you have only worked there for 6 months is just bad form.