The Centers for Medicare & Medicaid Services (CMS) recommend that practice keep all relevant meaningful use attestation supporting documentation (in either paper or electronic format) for a minimum of six years after attestation. This includes the records used to complete the Attestation Module responses. Attesting to having met the meaningful use requirements is certifying to the federal government that you are in compliance with the meaningful use program criteria and are eligible to receive federal incentive payments. CMS has the authority to conduct audits in the future to recoup erroneous payments and ensure government funds are not being distributed inappropriately.
Make sure you are in complete compliance with the meaningful use requirements.