CASES UNCONNECTED TO FINANCIAL AID OR EDUCATION
A good rule of thumb is that a law favoring or burdening religion or a specific religious group in particular will be invalid, but a law favoring or burdening a larger segment of society that happens to include religious groups will be upheld.
If a display of the 10 commandments is shown to have a predominantly religious purpose, it violates the establishment clause, otherwise they may be displayed.
If the gov't maintains a holiday/xmastime display that does not appear to endorse religion, the display will survive review under the Lemon Test. If it includes religious and non-religious decorations, it will still pass. If it includes only a nativity scene, it will violate the establishment clause.
A state may not force employers to grant all employees an absolute right to refrain from working on their sabbath, because the primary effect of such a law is to advance religion. However, a state may require employers to make reasonable efforts to accommodate employee religious practices.