IF OR Statement

Hello,

I have a pretty simple question. I am using Query editor to add a Custom column to my table. This column is called "True cost" and adjusts costs based on the Warehouse code by a factor of 2.5. When I use one warehouse code everything works fine, when I add 2 or more the logic doesn't work. I don't receive a syntax error but when the query runs, a following message comes up "The name OR was not recognized". What am I doing wrong and how to correctly make IF OR statement ?

This formula works = if [Warehouse Code] ="XXX" then ([Total Transacted Cost]/2.5) else [Total Transacted Cost]

This formula doesn't =if [Warehouse Code] =OR("XXX", "YYY", "ZZZ") then ([Total Transacted Cost]/2.5) else [Total Transacted Cost]

Thanks,

Andrey