I'm conducting an audit for a retail client and need to optimize the process for verifying sales transactions to prevent fraud. What are the best practices for sampling and analyzing large volumes of sales data efficiently?

I've been tasked with auditing a retail company that has high-volume daily sales across multiple locations. I've tried using random sampling in Excel, but it's slow and I'm concerned about missing patterns or anomalies. I'm looking for methods to improve accuracy and speed, especially with tools like audit software or data analytics. Any tips on setting up a robust audit trail or integrating with their POS systems would be helpful.