Implement half away from 0 rounding
Q (29 Characters)

{("i"$x*10 xexp y)%10 xexp y}


Sample usage

{("i"$x*10 xexp y)%10 xexp y}[1.23456;4]


Works by multiplying your x input by 10 to the power of your y input, casting to an int and then dividing again by 10 to the power of your y input.