It will be 私は天ぷらを食べたことがありません。 たform+ことがありますmeans something that you ever did. Andたform+ ありませんis the negative form ofたー あります and that means "haven't ever". Best regards, I Made

"I have never eaten tenpura" means "私は天ぷらを食べたことがありません". On the other hand, "I have never tried tenpura" literally means "私は天ぷらを食べてみたことがありません". The latter Japanese sentence sounds a bit redundant, though. So, you usually just say "食べたことがありません" even for the second English sentence.

I usually use, 天ぷらを(まだ)食べたことはありません: I have not eaten Tenpura, yet. Try is like 挑戦する or 試す、Japanese has the sentence 試食する, but it's like try some food samples at supermarket before purchasing.