[bogomipz]

I'm confused, what is the purpose of the automatic lottery ticket tied to a sales receipt?

I've spent time in Portugal and was never asked if I would like to participate. Is it only certain types of store or receipts?

[PedroBatista]

To combat tax evasion/parallel economy. The rationale goes: People want to get deductions and maybe even win a car, so they demand a receipt from business. That means said business can't keep that transaction off the books.

"Is it only certain types of store or receipts?"

Every business.