I have a friend who worked at his store in the USA selling beer and pork. Then he decided to quit selling these things and he did. But when he returned from Yemen to the USA, he found that his store where he was working had many problems, bills, taxes and other expenses. He cannot work another job until he pay this money. Can he still work at that store until he pays these taxes? He has a lot of responsibilities and he really wants to quit working at this store.

Praise be to Allah, the Lord of the World; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Selling wine and pork is forbidden, and this ruling is well-known in Islamic Sharia.
Therefore, everyone who has indulged in such business should make sincere repentance. The main condition of a valid repentance is to give up that sin totally.
Continuing to work at that shop is permissible till he settles all his due payments provided he does not sell any forbidden thing such as wine, pork, etc. He is allowed to sell only the Halal products. Investing money in Haram is absolutely forbidden. No doubt that Halal is fully sufficient for a Muslim without dealing with Haram.
Allah Says (interpretation of meaning): {… And whosoever fears Allâh and keeps his duty to Him, He will make a way for him to get out (from every difficulty). And He will provide him from (sources) he never could imagine …}[65:2-3].
Know that whoever gives up something for the Sake of Allah, Surely Allah gives him better than what he has left.
Allah knows best.