Round the values down at the places noted.

100.009 at hundredths place

Round 100.009 down at 1/100s place.
Rounding digit is 0.
For all the digits right of the hundredths place:
Drop those to the right of the decimal place.
Zero-fill those to the left of the decimal place. Result is 100.00

Note: For purposes of significant figures the
result is 100.00. For all other purposes drop the trailing zeros to give 100.