请问 一般跟老外做生意找钱用英文怎么表达

It costs you 90.5 yuan,I get your 100 yuan,Here is the change 0.5 .

The total is ninety O(发字母O的音) five, out of a hundred, and five-cents is your change..
一般的口语就是这么说...

ninety fifty please~

然后一般没有人说收了100元~因为老外懒得听~如果你是在想说: you payed by 100 bill.

here is your fifty cents change.

在国外你因该说：Keep the change.
0.5元当小费，免得外国人说咱小气。