Resizing vs Scaling
So you've got something small and you'd like for it to be larger? If the object has effects such as a border or rounded corners, they will actually not be scaled with the object if you just drag it larger.
Now instead of having the same thing but larger, we have a very different looking object. Not good. So this time let's instead use the Scale button on the toolbar.
When you scale an object this way, you may use either desired pixel dimensions or a percentage to multiply by. The best part is written at the top of the dialogue box; "... Style attributes such as border thickness, shadow size etc will be scaled appropriately." The result will therefore be a larger version of the original.
Success! Simply a larger version with properly scaled effects, including the radius of the rounded corners.