In this question we learn that toward and towards are interchangeable, but that the former is somewhat more typical of U.S. English and the latter of British English, although there is some indication that this does not always hold true.
But how about actual use? Being a non-native speaker, I cannot completely trust my intuition about what "sounds right". Is it true that toward sounds more formal than towards to a native English speaker? Does it vary between different variants of English? Should I use one in academic text and the other in casual communication? What are the nuances? In summary, how should I choose which one to use if I want to be consistent in my writing style? I'm looking for intuition for different kinds of situations.