At work - I am a cashier, and there are Christmas cards with shirk on them "Jesus is God - and Loves You" etc... If a customer brings these to me, and I ring him up and put the money in the register - am I a kaafir? I hate the shirk, ......., ......, am I a kaafir?
As long as you are a true believer, who believes in the oneness of Allah, the Most Gracious, and who has not committed any act that would expel you from the religion of Islam, and as long as you hate ! shirk and (the blasphemy of) Christianity, then you are a Muslim and not a kaafir. However, you must realize that it is unacceptable for a Muslim to aid or abet the kuffaar (non-believers) by any means or medium relating to the celebration of their holiday occasions. This would encompass selling items that are used in their celebrations. Sheikh ul-Islam Ahmad ibn Abdul-Haleem ibn Taymiya (may Allaah have mercy upon him) in his classic and monumental book entitled Iqtidaa’ Al-Siraat Al-Mustaqeem Mukhalafat As-haab Al-Jaheem (In Pursuit of the Straight Path by Contradicting the People of the Hellfire) said:
"As for a Muslim selling to them (the non-believers) items that they use to celebrate their holiday occasions, such as food, clothes, perfumes, etc., or offering such items as gifts, is a way of helping them celebrate their "unlawful" holidays. This idea is based on the fundamental principle that states that it is unacceptable (for a Muslim) to sell the kuffaar grapes or juice which they will use to produce wine or alcoholic beverages. By the same token it is also unacceptable (for a Muslim) to sell them weapons that will be used to fight Muslims.
He then presented an argument presented by Abdul-Malik bin Habeeb (among the scholars of Al Malakiyya madh-hab) in which he said "Do!n’t you see that it is forbidden for a Muslim to sell Christians any item that benefits or concerns their holidays? Not meat, nor food (eaten with bread), nor clothes, nor should they even be lent an animal (to ride on). They should not be helped in any way that relates to their holidays because this would be considered a form of glorifying their shirk (blasphemy) and supporting them in their apostasy and disbelief…." Al-Iqtidaa’ p. 229, 23, Dar Al-Ma’rifah printing, tahqeeq (verified and edited by) Al-Faqiy.
We ask Allaah to help you be firmly established on the truth, and to ward you away from wrong and falsehood, and to provide you with good and righteous means of living.
May the peace and blessings of Allaah be upon our Prophet Muhammad .