我昨天去饭店吃饭，我结帐的时候那个收钱人问我发票的事情。 收钱人，we say,收银员

如果你不要发票，可以少付点钱，因为这样商家就少交了你在他们那里的消费的税。 其实就是变相的帮助他们逃税。

发票就是receipt or invoice,证明你在他的饭店吃饭，如果你是用公款消费的话，还可以拿这个receipt去报销（有点corrupt,but that is how it works）

发票 Invoice An invoice or bill is a commercial document issued by a seller to the buyer, indicating the products, quantities, and agreed prices for products or services the seller has provided the buyer. From the point of view of a seller, an invoice is a sales invoice. From the point of view of a buyer, an invoice is a purchase invoice. In your situation,it's a proof of your consumption in the restaurant.If you take the invoice from restaurant which means the restaurant have to pay taxes.If you just get receipt 收据，the restaurant do not need to pay taxes.Usually in China if they issure you an invoice,the invoice included the taxes you paid for the meal.

you say ：ca ni ma。