A group of receipts is commonly called a Wad. Other collective nouns you may see include Pile and Littering.
A collective noun for receipts is clutch. A clutch of receipts represents a group or collection of these documents typically obtained in order to validate transactions or purchases made by individuals or an organization. Clutches are often kept by individuals for personal record-keeping, or by businesses for accounting and tax purposes. This collective noun captures the idea of organizing and holding together various receipts that collectively represent the financial activities and expenses of a person or entity. Much like a clutch bag holds together different items, a clutch of receipts encapsulates these documents which chronicle financial movements.
Known collective nouns for Receipts include: