Im working in a dealer i want to know if its legal for them to not charge you the right amount of taxes that are supposed to be taken out.

If you are an employee, the employer generally withhold income tax, and social security and medicare, based on the W4 you fill out and provide to the employer, Therefore, generally, if there is an error in the amount of withholding, it is due to you incorrectly filling out the W4. You should check with your employer, and possibly update the W4 he has on file for you.