What's the best way to implement an Entry control that uses a percentage or currency format?

I've got a number of Entry controls that are bound to properties of type decimal.

Percentages are shown as decimal numbers, e.g. 10% is shown as 0.1 and currency is lacking the currency symbol.

I tried using a converter for each and it nearly works, but it causes the selection to keep jumping around like it's being updated for every key press.