Is there a calculator or some tool (I tried to find one on the internet with no luck) that can help to figure what % of taxes will be taken out of commission checks, if I know the gross amount I will be getting?

You don't want to know taxes you want to know withholding rates. This is a common misconception but people do not pay their taxes until they file their annual return. What is taken out from their regular paychecks is withholding which is an estimate of the taxes that will be due based on amount paid and W4 info.

So, if you search for Withholding tables, you should find the info you want.

Scott:

Actually, income and other taxes are paid by the employer (usually monthly) using the monies withheld from the employees' salary/wages.

The annual tax return is actually a reconciliation of all income earned and a report to the government on said income on which taxes are assessed, againt which the withheld taxes are credited. Any excess withholding is the refund. Any shortfall is the balance due that is to be sent with the tax return.