At a Mininum
The IRS has three years to audit individuals for what they believe to be "good faith" errors in filing. Therefore, at a minimum, all receipts should be saved for at least three years.
To Be Safe
Although the IRS only has three years to audit "good faith" errors in filing, they have up to six years to audit individuals if they suspect the taxpayer under-reported their income by more than 25 percent. Therefore, you could need your receipts for up to six years.
Ultimately, it would be wise to keep all receipts for seven years to ensure you have all the needed records in any audit scenario.