To what extent are you required or expected to tip, when you go to restaurants in Thailand?

For example, I went to a restaurant in Thailand and the bill was 175 baht, but I gave 180 baht.

Would this tip have been insulting, or would it have been okay? Am I expected to give a tip?

(Note: This restaurant looked like a family owned restaurant, where the people who worked there were in the same family)
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