Some Cells look different when spreadsheet is viewed by others

I have a very simple one-page spreadsheet, with 8 columns. Only one column is formatted as "Accounting" and contains monetary values from $175.00 to $6,000.00. The sheet looks fine when I finish with it, but when my boss looks at it, some of the monetary cells contain #####. I thought this might be caused by a column being too narrow to show all the information, but on the most recent occasion of this, the only cells with the #### signs were the lowest dollar amounts (in the hundreds, rather than thousands). I'm not sure what's causing this, but I'd like to get it resolved so my boss can read the full sheet.

In the last instance, I went in and made the font smaller for those 3 cells and that corrected it. But it just seems like an odd way to fix this.

There are no calculations in the cells in question... only numeric values.

Does anyone have any suggestions?