Adam was created perfect, he was not designed to taste death.
Those are two big statements, which aren't expressed in the Bible. At the same time, Adam did sin and he did die because of his sin. That alone quite strongly suggests he was neither perfect nor designed not to taste death.
Adam was alive thanks to the three of life, which was not part of his being but outside of him (Genesis 2:9). That means he was, in fact, designed to taste death, but didn't deteriorate as long as he ate from the tree of life. As soon as he was banned from it (Genesis 3:22-24), he deteriorated until death.
It would be rather remarkable that omnipotent God created first man, perfect man, with intention for that man to live forever, and then that same man both sinned and died. Quite remarkable that omnipotent God creates something with one purpose, and then said creation messes with God's plan and becomes opposite of what God intended it for. Thankfully, Bible says that's not how things are (Proverbs 19:21, Proverbs 16:9, Proverbs 16:3, Jeremiah 10:23, James 4:13-16, Isaiah 46:10, Psalms 115:3, Philippians 2:13, Proverbs 16:4, Job 14:5, Proverbs 16:33, Psalms 33:10-11...).
When Adam explains himself to God after he sinned, what does Adam do? He exclusively blames God and Eve for the bite he took (Genesis 3:12). Doesn't seem like perfect behavior of a perfect man, I'd say. And what standard of perfection is that if all it takes is a bite to crumble it?
What's the real answer, then, as it seems to be revealed in the Bible? It's this - that God created Adam and Eve with purpose for them to sin, as a start of His plan for adoption.
To the OP:
Sorry for derailing the thread a bit... Here's my answer to your question.
I think Jesus took on Himself penalty for all sins for all who are saved. I think it was an unimaginable torturous experience outside of our realm. We saw Jesus on the cross, but Him taking penalty for people's sins was not happening in our world, but in other realm, just as penalty for unbelievers doesn't happen in this world, but in hell. I don't think Jesus took on penalty for some abstract sins, but for precise number of sins, for precise number of people. God reveals Himself through the Bible and natural world as God of precision, so I think there was a precision of Jesus' payment for sins too.
(I just realized this was an old thread, reawaken by somebody recently...)