function floor10( x ) {
	return addon( x );
}
Rounds a numeric value to the nearest power of `10` toward negative infinity.

@private
@param {number} x - input value
@returns {number} rounded value

@example
var v = floor10( 3.141592653589793 );
// returns 1.0

@example
var v = floor10( 9.0 );
// returns 1.0

@example
var v = floor10( -0.314 );
// returns -1.0