The below links will help you track how the United States is spending money.
USASepending.gov
Provides access to spending by all agencies, including specific grants and loans provided by the federal government. Data goes back to about 2010 in most cases.
Financial Report of the United States
Similar to company's annual report, the Financial Report of the United States provides an overall view of the government's financial health, including future projections. From 1998-
Treasury Bulletin
Provides receipts by source for the last five years and last 12 months by agency.
Monthly Treasury Statement
From the Financial Management Service of the US Treasury, summarizes the financial activities of the federal government and off-budget federal entities.
Combined Statement of Receipts, Outlays, and Balances of the United States Government
The official publication of receipts and outlays for the fiscal year, from 2001-. Previously called the United States Government Annual Report, and available in print or via this same link.
Government Accountability Office Reports
Previously known as the General Accounting Office, the GAO is the "investigative arm of Congress," and studies how federal money is spent.
Openspending.org
Track public spending from around the world on various projects.