When we estimate, we do not carry out exact calculations.
We work things out ROUGHLY.
7 is roughly 10
48 is roughly 50.
389 is roughly 400.
The Battle of Hastings in 1066 was roughly 1000 years ago.
960 grams is roughly 1 kilogram.
Six 18 cm long pencils placed end to end will stretch roughly 1 metre in length.