It is always a good idea to keep your receipts. However, it is not necessary to have them to enter the amount on your return if you know for a fact you paid it. In the unlikely event you are audited, you would need them.
As stated by leeloo, it is always a good idea to have backup documentation for deductions you are claiming as part of your tax return.
As you may know, you are allowed to claim up to $300 in unreimbursed expenses for books, supplies, and equipment used in the classroom.
To go to the section of the tax return to enter this information, use these steps: