L.A.
Yes it's common. My son does this, not to keep himself out of trouble but to try to have things be the way he wants them to be. It's more like wishful thinking out loud.
there's a great book called Nurture Shock (by Po Bronson) that has a whole chapter on lying. You can search the internet and find a large excerpt from the chapter to read. The basic concepts for dealing with lying are: don't lie yourself. This includes white lies. And point out that you know that was a lie, say that lying isn't okay and then go on from there with the truth.
p.s. His book is a national bestseller and was based on a great deal of scientific research on what kids & families do and the results from their actions. He then gives some good (and maybe surprising) guidelines on what "works". It's VERY informative and an easy read. (or listen via audiobook)