import math


def specify_significant_figures(float_value, num_sig_figs):
    """Round float_value to num_sig_figs significant figures."""
    try:
        # Find my_mult, my_exp such that float_value = my_mult*10^my_exp
        #   such that  1. <= my_mult < 10.
        my_exp = math.floor(math.log10(abs(float_value)))
        my_mult = float_value/(10**my_exp)
        return round(my_mult, num_sig_figs-1)*(10**my_exp)
    except ValueError:
        return 0