Publication 334 straight from the IRS.gov website! Hope this helps!
Inventories
Generally, if you produce, purchase, or sell merchandise in your business, you must keep an inventory and use the accrual method for purchases and sales of merchandise. However, the following taxpayers can use the cash method of accounting even if they produce, purchase, or sell merchandise. These taxpayers can also account for inventoriable items as materials and supplies that are not incidental (discussed later).
A qualifying taxpayer under Revenue Procedure 2001-10 in Internal Revenue Bulletin 2001-2.
A qualifying small business taxpayer under Revenue Procedure 2002-28 in Internal Revenue Bulletin 2002-18.
Qualifying taxpayer. You are a qualifying taxpayer if:
Your average annual gross receipts for each prior tax year ending on or after December 17, 1998, is $1 million or less. (Your average annual gross receipts for a tax year is figured by adding the gross receipts for that tax year and the 2 preceding tax years and dividing by 3.)
Your business is not a tax shelter, as defined under section 448(d)(3) of the Internal Revenue Code.
Qualifying small business taxpayer. You are a qualifying small business taxpayer if:
Your average annual gross receipts for each prior tax year ending on or after December 31, 2000, is more than $1 million but not more than $10 million. (Your average annual gross receipts for a tax year is figured by adding the gross receipts for that tax year and the 2 preceding tax years and dividing the total by 3.)
You are not prohibited from using the cash method under section 448 of the Internal Revenue Code.
Your principal business activity is an eligible business (described in Publication 538 and Revenue Procedure 2002-28).
Business not owned or not in existence for 3 years. If you did not own your business for all of the 3-tax-year period used in figuring your average annual gross receipts, include the period of any predecessor. If your business has not been in existence for the 3-tax-year period, base your average on the period it has existed including any short tax years, annualizing the short tax year's gross receipts.
Materials and supplies that are not incidental. If you account for inventoriable items as materials and supplies that are not incidental, you will deduct the cost of the items you would otherwise include in inventory in the year you sell the items, or the year you pay for them, whichever is later. If you are a producer, you can use any reasonable method to estimate the raw material in your work in process and finished goods on hand at the end of the year to determine the raw material used to produce finished goods that were sold during the year.
