Why do Lori and Jeannette name their piggy bank “Oz”?

Oz is where they keep their escape fund. Oz represents a place to escape to. They needed to have faith in this place like the characters in "The Wizard of Oz" did. Jeannette relates to the character of Dorthy (from Wizard of Oz) in that they are both looking for a home, or a place they can feel secure.