We are an existing 501c charitalbe organization in Minnesota. Are we required to charge sales tax on prepared foods during a fundraiser

Let's put it this way: 501 (c) (3) doesn't exempt you from paying taxes, federal, state, or local. It allows donors to deduct their donations, made to your organization, from their federal income tax.

Check with your state or local taxing authority to see if there is an exemption form the sales tax for your organization.

Are you giving away the food and asking for a donation ? OR are you selling the food.

I will be honest most do not, in fact most 501c3 do not even have sale tax numbers since they as a whole do not sale items, others who have book stores, or thrift stores often have tax numbers. The sales tax is based on State laws.