1
general::
Phrase(s): round something out
to complete or enhance something. • We will round the evening out with dessert at a nice restaurant. • They rounded out the meal with dessert.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
1. See ROUND OFF, def. 2. 2. Grow or develop to a round form, as in The tree was spindly when first planted, but it has since rounded out nicely. [c. 1900]
American Heritage Idioms