Tax audit thresholds and presumptive income rules govern compulsory audit, filing of reports, and low-cash business relief. Mandatory tax audit applies where business turnover or professional gross receipts exceed the prescribed limits, and also where a taxpayer covered by presumptive or deemed-profit provisions claims profits lower than the statutory amount. A higher business threshold is available for low-cash businesses if cash receipts and payments stay within the prescribed percentage limits. The audit report must be furnished by the specified date in the prescribed form, and compliance is sufficient where audit is already required under another law and the prescribed reports are furnished on time.