What a brilliant site you have!!! I love it, especially as it saves me hours and hours of hard work. Others who haven't found your site yet don't know what they are missing!
6.NA.1 – Apply additive and simple multiplicative strategies flexibly to:
6.NA.1.a – Combine or partition whole numbers, including performing mixed operations and using addition and subtraction as inverse operations
Samples: Write numbers – to 100 000. Reading numbers – to 100 000. Comparing numbers – to 100 000.
Number and place value
ACMNA099 – Use estimation and rounding to check the reasonableness of answers to calculations
Samples: Two digit addition (estimating). Division (estimation) - 1. Rounding numbers to the nearest 10.
You can go to an overview of all the curricula here.