Javascript: find closest number
<p>i would like to find rounded nearest number in javascript e.g.</p>

<p>10 --> 10</p>

<p>11 --> 10</p>

<p>12 --> 10</p>

<p>13 --> 15</p>

<p>16 --> 15</p>

<p>17 --> 15</p>

<p>18 --> 20</p>

<p>19 --> 20</p>

<p>20 --> 20</p>
