numbers in thousands W/ Comma

I've been trying to figure out a way to have numbers round to thousands with commas (to one decimal point), yet everytime I try this it will show the number as the true number in thousands except it does not show a comma.
For example, in my spreadsheet, I want to round $1,234,567.89 to 1,234.6----however, if I use the custom formating in the cell "0.0," it will just show "1234.6" and NOT "1,234.6" like I would like. Maybe someone knows a way to accomplish this seemingly easy task, yet I JUST CAN'T FIGURE THIS ONE OUT!! HELP!