When asked to round a number, you need to know how many decimal places to round it to, or how many significant figures, or to the nearest ten, or whole number, etc.
This has not been stated so I’ll round it in several ways:
Nearest whole number: 4
1 decimal place: 4.2 (2 significant figures)
2 decimal places: 4.23 (3 significant figures)
3 decimal places: 4.229 (4 significant figures)
The rule for rounding is that, if the next digit to the right of the one you are trying to round is 5 or more, then you add one to the one you are rounding to. So for 4.2291 rounded to 2 decimal places, the digit in the second decimal place is followed by 9, which is greater than 5, so the 2 in the hundredths place becomes 3.