Just how long you should keep records is partly a matter of judgment and a combination of state and federal statutes of limitations. Federal returns can be audited for up to three years after filing, (six years if underreported income is involved). So, all records substantiating tax deductions should be kept at least that long.
Cancelled or Substitute Checks, Credit Card Receipts, Paid Invoices, Bank Deposit Slips, Bank Statements, Tax Returns, Employment Tax Returns, Expense Records, Financial Statements, Contracts and Meeting Minutes.
Note: Computer-Maintained Records are the same as manually kept records.