[j0hnik]

function recalc(id) {
	var el = $('input[name='+id+']');
	var current = el.val();
	var min = 0;
	var step = el.attr('step');
	var max = el.attr('max');
	var avalible = $('#v-sin > input').prop('checked');

    // Округляем кратно step (количества товаров в упаковке)
    current = Math.ceil(current/step)*step;

    if (current < 0) current = 0;
    if (current > max && avalible) current = max;

    el.val(current);

  }