A barcode scan is a lookup, not magic: the scanner reads black bars into digits, the POS matches digits to a SKU record (name, price, tax class, stock), and the bill adds price − discount + GST. When any link breaks — wrong barcode on the shelf, stale price, missing tax class — the shop bleeds margin one sale at a time.
SKU vs barcode (in 30 seconds)
Barcode: the printed digits (often the manufacturer's EAN-13).
SKU: your internal code, e.g. RICE-5KG-001. One product can carry several barcodes (supplier packs) but has one SKU.
Rule: scan → SKU → price/tax/stock. Never price from the barcode alone.
Inclusive pricing: shelf price already contains tax; back it out for reports (1,000 ÷ 1.18 ≈ Rs 847 + Rs 153 tax).
Exempt items (basic foods): 0% with the exemption printed, not silently skipped.
Receipt anatomy (FBR-ready)
Shop name + NTN, item lines with tax class, subtotal, discount, GST total, grand total, payment method, and a QR/digital copy. If a receipt lacks any of these, the invoice won't survive an audit.