First, writing the number in dollars and cents OR rounding up/down to create a whole number is acceptable reporting per the IRS, but the form must maintain consistency throughout the return. There are two options, as recommended by the Internal Revenue Codes & Regulations Handbook to write a negative amount:
1) Place parentheses, e.g. (9000), around the number OR 2) Place a minus sign on the left side of the figure, e.g. -9000. This indicates the entry is a negative number.
Remember to deduct the negative amount from the items affected by the listed negative entry.