Correction, the Commandments that are the cornerstone of western law are:
Don't kill anybody
Don't lie
Don't steal
Honor your parents
Don't commit adultery
And those are terrific guidelines for everyone to follow. So much so that they have been turned into laws. The others have little significance to non-Judeo-Christians and have no place in a government building. Or at least no more place than a quote from the Koran saying that infidels should be killed and their women raped.
the basis of western law is largely roman.
christianity has played a very minor role. what contributions it has made over the years have mostly been shed by now as gross infringments of civil liberty (miscegeny, contraceptives, "blue laws", prohibition, gambling, adultery, etc.)
the 10 commandments have played even less of a role that christianity in general - in fact they have played no role. the only commandments mirrored at any time in US law were those already well established in western tradition before the rise of christianity.