Answer:
No, this does not violate the First Amendment's freedom of religion because the private employee does not need to abide by the rules of the Amendment.
Explanation:
The First Amendment to the United States Constitution includes numerous rights of citizens including the freedom to practice any religion. This allows a citizen to follow any faith irrespective of what others may base their beliefs in.
Accordingly, working in a retail site is a case of private sector work. And in working there, the employee doesn't have to abide by any of the First Amendment rules. Moreover, the order by the boss to not talk so much while working has nothing to do with freedom of religion.
Therefore, this scenario does not violate the First Amendment's freedom of religion.