Taking the liberty to use graphics to illustrate Ruel's tutorial. I want to make it clear in my head of what is an excellent idea he has had. I hope you don't mind Ruel and I hope this is what you meant. Using text may not be the best example but...
An irregular object. In this case some Arial text in a 400 wide by 140 high document.
1.) Create your object at full size
2.) Shrink your object, holding the control key, to something a bit smaller - about 3/4 size.
3.) Create a Dynamic Offset (Path->Dynamic Offset) and pull the handle to make it larger until you're happy with the size of the rounded corners.
4.) Click on the select cursor and resize, again, holding the control key, to the size you need it.
Thanks Ruel, neat trick.