Function of "也" in "一点儿也不喜欢"
Both “也”  and "都" in “一点儿也不喜欢” / “一点儿都不喜欢” functions as the adverb "even" (used to emphasize something surprising or extreme)

"一点儿也不喜欢" = "not liking it even a little"

Similar example: 

"一元也不值" = "not worth even one dollar"

"(最后)一元也需要还清" = "have to payback in full even (the last) one dollar"