In the state of Massachusetts a not-for-profit has several things they need to know.
You can make purchases without paying for sales tax. The state issues the ST-2 certificate to not-for-profits every ten years. You should be able to simply bring your certificate to a grocery store and be able to exclude the sales tax. Other vendors should honor it as well. If you believe you think it will be difficult to obtain the exemption during the purchase, then you can fill out a larger form, the ST-5.
Please see below from the state
https://www.mass.gov/administrative-procedure/ap-101-exemptions-from-sales-tax#101-1-3-use-of-the-certificate-of-exemption-form-st-2-sales-tax-exempt-purchaser-certificate-form-st-5-and-contractor-s-sales-tax-exempt-purchase-certificate-form-st-5c-
You need to file by paper with the Attorney General’s Office. Most clients are surprised when we tell them that the AGO never received their paperwork. You need to sign the paper return and send it into the state, along with various attachments.
You also need to file with the Secretary of the Commonwealth’s Office. Yes there are two places to file. This second one costs only $18.50 a filing for each year.
The state also seems to be more lenient with the tax rules of not for profit entities. From personal experience, it appears that the state has a number of rules for each entity, however when it comes to not for profits they are more easy going. They have created filing rules that they simply do not enforce for the good of the community.