Allow address abbreviation in the sign up form or when adding address i.e.St. and not Saint and won't affect the cheapest shipping cost.
The norm is to write St Kilda Road. Not Saint Kilda Road. Even in the Melway or Google maps etc, it is known as St Kilda Road or St Kilda as a suburb. I may be able to change after a customer places and order, but the initial order will still be placed by a customer using St Kilda.