I have been told by various people that working in grocery stores is haram because of the cigarettes and alcohol sold. Is this true?

please find the verdict on selling Alcohol issued by AMJA(Assembly of Muslim Jurists of America)
http://www.amjaonline.org/fatwa-23386/info
Working at a grocery stores is Halal and allowed. What Muslims Iknow do is that they kind of have a mutual agreement with their supervisors to ask a non Muslim co worker to ring up the customer who is buying alcohol/tobacoo products. As long as you try your best to avoid the transaction by all means, then you are okay.
If the need to ring up a customer arises because of the absence of a co worker and being alone at the store and you think the customer will be offended if you ask him/her to be rung up by the main cashier at the front of the store, then you are still okay to do the transaction as this is not considered your main job and it happens rarely. However, if these type of transactions are forced upon you on daily basis, then you might want to consider a different kind of job.

Halal jobs are jobs that basically don’t sell or provide services to people that are considered prohibited in our faith.