I sold my home last year but do not have the original closing paperwork. I bought the home in 1998 and refinanced in 2005. Can I use refi information instead?

No, your refinance information is not the same as your original home purchase information.  If you cannot find your refinance information, you can try contacting the recorder of deeds in your county as they have the historical information for selling/purchase price.  However, they generally don't have your other costs such as closing costs. If you find your purchase price, you  may be able to estimate some of your other costs based on the purchase price of the home.  You could also contact the title company you used or the bank where you had the original loan as it is possible they still have the original documents.