When someone turns 10, 20, 30, 40, 50... it is common in Germany to say that they are celebrating their "runder Geburtstag" which is usually celebrated in a larger way, inviting a larger circle of people, etc.
When I translate this into English, I usually say, "she is celebrating her rounded birthday" but I don't think people really understand that out of a German context.
Is there a common expression for this in English?