"This fruit does not taste good at all."
Not really. Since ぜんぜん is used to negate the おいしい, they must be linked in a fixed sequence, u can also swap it for とても,すこし,ちょっと,あまり, to modify the degree of おいしい
But oishikunai already means not delicious. You put zenzen on top of that and it seems to be the opposite
I think とても is usually used with positive statements, whereas ぜんぜん is usually used with negatives.
They have opposite meanings, the first being "very" and the second being "not at all"
Doesn't it mean "at all", instead of "not at all". The negative here is already covered by the adjective, and i imagine ぜんぜん comes from 全, ぜん, meaning "all" or "entire"