I think they're actually a tiny bit different, but I think ING (at least) is compounded daily and credited monthy. So, $10,000*(.0300/365daily percentage rate)*31days in a month = about $25.50 a month in interest. Then that $25.50 would be added to your account so your $10,000 would be $10,025.50 the next month. The "real" math is a bit more complicated, but I think this estimate is within a few cents. If you need perfection let the board know and I'm sure somebody (I'm going to bed for the night, so it probably won't be me) will give you the full story
