According to the natz. guide document checklist for applicants for naturalization on the basis of marriage to a U.S. citizen the following section applies:
4. Documents referring to you and your spouse:
• tax returns, bank accounts, leases, mortgages, or birth certificates of children, OR
• IRS-certified copies of the income tax forms that you both filed for the past 3 years, OR
• an IRS tax return transcript for the last 3 years.
From the three options, the last one, the IRS tax transcript is the easiest one to provide. I sent copies of IRS tax transcripts for our joint returns. The I/O did not ask for the originals, however I had them with me at the Interview.
I had also included copies of joint bank accounts in the application. At the interview the I/O asked for more current (within the last couple of months of the interview) bank statements, mortgage statement/lease, papers etc. So take the originals of what ever you include in your application packet, and also take some current statements at the interview.
All the best.