The TI matches the spreadsheet in both Open Office and NeoOffice (if you put it in as =6/2*(1+2))
I think my math teacher taught me to do parenthesis first, then multiplication/division left to right. That's six divided by two (three) then times three for nine.
I do recall seeing the order of operation that leads to the Casio answer, but I don't remember where I saw it or what circumstances they said it was the preferred method.