Rounding to nearest 100

Question

First number needs to be rounded to nearest second number. There are many ways of doing this, but whats the best and shortest algorithm? Anyone up for a challenge :-)

1244->1200
1254->1300
123->100
178->200
1576->1600
1449->1400
123456->123500
654321->654300
23->00
83->100

Answer 1

Ruby's round method can consume negative precisions:

n.round(-2)

In this case -2 gets you rounding to the nearest hundred.

Answer 2

For input n:

(n + 50) / 100 * 100 

using integer division.

Note that many languages/libraries already have functions to do this.