You may want to see if your employer will issue corrected W-2s for those years showing the cash tips. You will have to pay tax on the tips and you may be subject to penalties for the late payment of tax and/or under reporting of income. You can amend your tax returns but the IRS may decide to look back at more than just the previous two years that you are amending to see if you had cash tips in those years also. If the IRS finds unpaid tax in prior years they will request that it be paid along with penalties and interest.