You wrote: I'm trying to identify the artist of a song I heard in a store recently.

It is a female singer, sounds like an indie-type girl group (Luscious Jackson/Throwing Muses style).
The only lyrics I can recall are either "If I Knew Now What I New Then" or "If I Knew Then What I Know Now".

The band is called The Wishing Tree. The song is "Fly".