Withholding taxes are easy to get right in a single transaction and easy to get wrong across a year. A monthly reconciliation keeps small differences from turning into a large correction.
Compare the payroll register with the withholding records, and the purchase ledger with the withholding certificates you have issued or received. Differences should be explained in writing, even when they are small.
Keep a short exceptions list: new vendors without a tax number, foreign payments and unusual allowances. Review it with the person who approves payments.
This article is general information only. Rates and treatments depend on the facts of each case; consult a licensed tax consultant for your situation.
This article is general information, not tax advice.