The rolled "R" in french is not a basis, there is no fixed rule about it. Some roll the R saying that that gives it greater linguistic authenticity ( as the R in Latin language is rolled ), some pronounce it just like in english.
It depends on regions and dialect. But as long as the meaning doesn't change, this is not a big deal.
I remember that my teacher told us in a phonetic lesson a funny story about that, one would say that the french king Louis 14 could not pronounce the letter R properly ( rhotacistic ) that's why linguists at that time made the rolled R a rule :)