Schools, governments, churches and some nonprofits can have this status. The bid documents state it, often in the instructions to bidders or supplementary conditions.
The rules vary a lot by state. In some states the exemption covers materials the contractor buys. In others it does not.
Find the tax statement in the packet before you price materials. Ask whether the owner will issue an exemption certificate. Tell your suppliers so their quotes match.
Check your state rules or ask your accountant. Takeoff Tool reads tax exempt status from the packet and shows the quote it came from.