Should I get a graduate degree to become an auditor?

Yes, because according to the U.S. Bureau of Labor Statistics, some employers would rather hire an applicant who has completed an advanced degree program, like a Master of Science in Accounting or Master of Business Administation.
Also, auditors who earn voluntary certification may experience more opportunities for career advancement.
Some programs also offer students the opportunity to utilize an internship to gain experience with an accounting firm or within the accounting department of an organization.