Let’s hear this straight from the horse’s mouth, the IRS.
How long should I keep my records?
You must keep records so that you can prepare a complete and accurate income tax return. The law does not require any special form of records. However, you should keep all receipts, cancelled checks or other proof of payment, and any other records to support any deductions or credits you claim. Keep them in a safe place. If you have to, scan them and keep the disc in a safe place.
You must keep your records for as long as they may be needed for the administration of any provision of the Internal Revenue Code. Generally, you should keep records that support an item of income or a deduction appearing on your return for at least 3 years from the date you filed the return. If you omitted income or need to establish basis for property, you will need to keep records even longer. In addition, you generally have 3 years from the date you filed your return, or 2 years from the date you paid the tax, whichever is later, to file a claim for credit or refund and will need to have records to support the claim.
This is directly from the gov site with personal comments.