Please note: there is no such a thing as a "00 BC" decennium. The first decennium in the first century BC begins with year 100 BC, continues with 99 BC, 98 BC and ends with counting throught the tenth year, wich is 91 BC.
The second decennium begins with 90 BC and ends with 81 BC. And so on.
Therefore the last decennium begins with 10 BC and ends with year 1 BC.
There is no "zero" year, the calculation going from the 31st of december of the year 1 BC to the 1st of January of the first year of the new era (which is year 1 "after he birth of Jesus", wich happened on December 25 BEFORE Christ), i.e. 1 AD.
However, the commong and widespread habit calculates the "10s BC" not as the years going from 10 BC to 1 BC, but from 19 BC to 10 BC. To avoid clashes and confusions a "leap" 00s years category was therefore created.