Can I just estimate the total value of all the items that I donated for tax deduction?

At the beginning of this year, I donated many stuff to the Salvation Army.  There are so many items that I just put "Clothes - 3 bags - Nearly New", "Shoes - 2 bags - Nearly New", and so on.  None of any single item worth more than $500.  However, I certainly cannot remember how many clothes and pairs of shoes there were.

Under TurboTax, may I just input "Clothes, Books, Handbags, Shoes, etc" under "Description" and an aggregate estimated value of $3,300 with "Comparable Sales"?  Do I need to mail the Salvation Army receipt to the IRS?

If audited, what can I do to prove the value?  Quite a lot of the stuff were almost new anyway.

Thank you.