Sure, here are the best answers underlined:

1. They **have** / are having a nice new white car now.
2. The price of our meal **includes** / is including tax.
3. I'm talking with my sister, but I don't understand / **am not understanding** what she's saying.
4. The cake **tastes** / is tasting good.
5. She **finds** / is finding it hard to learn Japanese.
6. My uncle **is** / is being a famous artist.
7. We **need** / are needing some butter to make cookies.
8. They look / **are looking** for a missing girl at the moment.