Do I need to report a $100 stock profit?

Yes, the IRS requires that all income be reported including when you did not receive a 1099.

Here's where you enter your 1099-B in TurboTax:

1. Open (continue) your return, if you haven't already
2. Locate the search bar. Search for 1099-B, then select the Jump to link in the search results
3. Select Okay! on the screen Time to kick off your investments! OR Yes on the screen Did you sell any of these investments? then Continue
   • If you see Your investments and savings or Your investment sales summary, select Add investments or Add more sales
4. When you reach Let's import your tax info, choose how you want to enter your 1099-B:
   • To import your form, select your brokerage or financial institution from the list. Enter your sign-in credentials for your account, then select Get my form
   • If you want to enter your 1099-B manually, select Enter a different way, then select your investment type on the next screen
5. On the following screens, answer the questions about your 1099-B
6. When you reach the Review your sales screen, the form you just entered should be listed
   • If you need to add another 1099-B, select Add another sale. Otherwise, Continue

See this link for additional information https://Where do I enter a 1099-B?