A certified copy and a notaried copy are NOT the same. So don't be confused with these two terms. A notarized copy is signed by any notary who only attest to the fact that the copy is the true photocopy of the document. That's all. A notary can notarize any documents (and signature) after seeing the true/actual copy of the document (or after seeing the true signature of the person). On the other hand, a certified copy is certified and given only the authority that issued that specific document...for example, in order to have a certified copy for a divorce decree then only the same court, that granted/heard that particular divorce case, can issue a certified copy of the divorce case. Similarly, in order to get certified copies of tax returns, only IRS can provide certified copies for tax returns. In order to get a certified copy of marriage certificate, one need to contact the same city registar where marriage took place.
A certified copy contains a seal/stamp with signature of the authority that issued the original document. A marriage bureau cannot certify tax records or anything else; rather only the marriage certificate that they have ever issued.
USCIS used to require submitting of notarized copies of everything 13 years or before, but not anymore. However, they do require certified copy of everything when there is a criminal matter involved.
Anyone can get anything notarized free of charge by going to their bank as banks always have a notary and they don't charge anything to their customers. On the other hand, certified copies cost money...from $2-$8 except tax returns as they cost a bit more.