This is general information, not tax advice — always confirm specifics with a qualified accountant. In the United States, the IRS generally expects a written acknowledgment for any single contribution of $250 or more, stating the amount given and whether any goods or services were provided in exchange.
The safest practice is to issue that acknowledgment for every gift, not just ones near the threshold — a receipt should include the donor's name, the date, the amount, and a clear statement like "no goods or services were provided in exchange for this contribution" when that's the case.
A sequential receipt number for every donation makes both auditing and donor questions ("did you get my check from March?") far easier to resolve than searching through a paper trail.
At year end, an annual giving statement summarizing every gift a donor made across the year saves both your treasurer and your donors significant time during tax season — and it's far easier to produce automatically from good records kept all year than to reconstruct in January.