[cshimmin]

In scientific notation (orders of magnitude is what matters here):

1.700e3 rounded -> 2e3

1.660e3 rounded -> 2e3

Put another way: if your bill for lunch is $16.60, wouldn't you just as easily call it $17? Or even $20, if you're feeling a bit imprecise?

[oxplot]

Yes, where I live, a lot of businesses charge you credit card surcharge of 2-3%. That’s $17 for a $16.60 priced item.