I switch back and forth between the 'OR' and 'OUR' on those types of words. Part of it is because when I was at work, any emails sent to customers had to have the 'American' spelling of words like that and also because I started programming WAAAAYYY back on the Atari 8bit computer systems. One of the commands in BASIC was SETCOLOR so my hand was sorta forced.
But I do know what you mean about dealing with USD$ amounts. Anyone that does any serious amount of purchasing online pretty much thinks in terms of USD. Fortunately, our dollar is so close to the USD now that exchange is negligible (right now ~10% premium).