Used coffee grounds are nearly neutral (I've seen ph stats that run from 6.2 to 6.9), so they won't acidify most soil. Coffee beans are acidic, but brewing the coffee removes most of the acid from the bean.

Slightly acidic soil is suggested for tomatoes 6 to 6.8. My soil is 7.3 and tomatoes thrive. If you have more alkaline soil, coffee grounds will help lower it, but not much. Once used coffee is grounds they have a PH of around 6.8.

Most all vegetables prefer slightly acidic soil - some more so than others. But you need to have a soil test done to determine what your soil pH is normally. That is the only way to safely know if any additional acidifiers need to be added. The soil test will advise how to correct your soil pH if it is needed.

Dave