The employer doesn't have a choice about whether or not to include your tips on your W-2. If they didn't include the tips, the W-2 is not correct. You should ask the employer for a corrected W-2 with the tips included.
If you cannot get a corrected W-2, you can enter them as unreported tips in TurboTax. First enter your W-2. After you enter your W-2 you will come to a screen that says "Do any of these uncommon situations apply to this W-2?" That screen has a long list of check boxes. One of the boxes says "Unreported tips." Check that box and continue through the interview to report the tips. The unreported tips will be added to the wages on your tax return. Form 4137 will be included in your return to calculate the Social Security and Medicare taxes on the tips, and these taxes will be added to the tax on your return.
Doing this will require you to upgrade to a paid version of TurboTax Online. You cannot file with unreported tips in TurboTax Free Edition.
