I have recently taken ober the HR position at my bank and the personnel files are not consistent. Are there any guidelines on what should be kept in an employee's file?

I just came across some helpful HR info HR Checklist

You will want to have centralized personnel files if you have a centralized payroll system. Personnel files should contain employment application, W-4, resume (if provided), copy of enrollment forms for health insurance, records of keys, cards, codes, etc. issued at beginning of employment, copy of salary actions, performance reviews, employees notices. I-9 Forms must be kept in a separate file.

To protect the company from discrimination. It's been a practice for years. I do not believe there are any Regs or Rules that state this is what you must do.

That is one importnat reason, but the second most important reason that if you are subjected to a I-9 audit by the USCIS, you will want them handy. Depending on the size of your organization, pulling I-9 information that is buried in 1000's of employees records is not a fun project.

If you have any health care related claims that contain diagnosis or treatment information that is personally identifiable, you will probably want to keep that in a separate area with restricted access (HIPAA).