Today 5 Euro Eypo is worth $6.38, but this changes daily. The best thing to do is to use an online currency convertor, XE is my personal favourite but there are many more to choose from.
The Euro endured a tough time in relation to the dollar originally, but there seem to be signs of the market improving in my opinion.
If you have a mobile phone, currency convertors are available as apps on all platforms and they are really useful to keep on your phone especially as most (XE for sure) give live results.
Therefore, if you are buying something in a foreign currency (perhaps on ebay or another website), you can work out how much you should be charged based on live exchange rates.
On XE, you can access a list of all the currencies you might be interested in, and can convert them very easily at any time. Honestly, once you have it, you will wonder how you got by without it :-)
Obviously, these type of apps are especially useful when on holiday in another country. Just be careful of data charges, as some apps tend to update in the background, which can be costly if you are on a roaming charge!