There are as many people who recommend fudging the amount as those who don't and both sides have strong arguments, in my opinion.
However, if you already know you don't want to do that then your only risk is that the customer backs out of the sale. But then you can always file a UPI because the customer doesn't want to abide by his own country's Customs policies.
Some people also recommend stating your own policies in regards to this subject within your listings in an effort to avoid this kind of grief.