Yes. However, the IRS want you to keep records of expenses. If you were to be audited, and could not provide receipts, the expenses could be disallowed.

Tips:

Paying by check or credit card provides proof of when the expense was paid, the amount of the payment, and the payee. Pay your vendors by check or credit card, since these tend to be your larger expenditures.

If you use cash for small expenditures, set up a petty cash system by writing a check to establish the fund. Save your receipts for petty cash whenever you reimburse yourself from the fund, and then write checks to replenish the fund when petty cash gets low.

If your records were lost due to circumstances beyond your control, such as by fire, you have a right to reconstruct your records as completely as reasonably expected. But if you were able to get duplicate records and did not, the courts will not allow estimation of business expenses here.

If there is no documentation, outside testimony can also be used as substantiation, but the IRS will review additional factors, such as the credibility of the witnesses and the amount and quality of the evidence.

If you are taking car expenses, on eof the questions you must answer is whether or not you kept records.

Recordkeeping

A written record of your business mileage could be a log book, diary or calendar that would include details about how, when and where a vehicle was used for business. It's smart to take notes about your destination and purpose of the trip each time you drive for business; this is really what the IRS is looking for.

Write down your odometer reading on the first and last day of each year. This way you can compute your business-use percentage on the total miles driven. Also, you can use your repair receipts to support your odometer reading.

In addition to orderly records, the IRS is looking for supporting documents of all listed property expenses. Show that your business expense records prove the following:

 1) The expense is your obligation.

 2) The expense is taken in the proper period. Your accounting period will affect this timing. For cash basis taxpayers, this means when the expense was paid. For accrual basis taxpayers, this means when the expense was incurred.

  3) The expense is a legitimate business expense. That is, the IRS will look carefully to determine whether it was a necessary and ordinary expense given your type of work.