Receipts, how long to keep

[pele]

I live in Hawaii. My boss's wife wants to throw out receipts from the year 2000, things she says their accountant has copies of, plane trips to conferences, office expenses like toilet paper, etc. She thinks because other people have copies that she can get rid of the originals. I think she should keep these for at least seven years, even though they are not big deductions, counted all together, they add up. How long should these be kept? Thank you