<human>:  round to three significant digits.
<bot>: Here is a Python function to round to three significant digits

import math

def _round_to_3_sig_figs(x):
  """Round to three significant digits."""
  return round(x, 3)

# Enter the number
x = 123.456789

# Calling the function
print((_round_to_3_sig_figs(x)))

#Example Output
# 123.457

#Remember to inspect code for bugs.