[Rise]

<input id="id_sq_pl" name="sq_pl" type="text" value="" />

<script>
document.getElementById('id_sq_pl').onblur = function() {
	if (/^(\d*[\.,]?\d+)?$/.test(this.value)) {
		this.value = ((Math.round(((this.value).replace(',','.'))*10)/10)+'').replace('.',',');
	} else {
		alert('Введите число');
	}
}
</script>