function selection_incremente_quantite(objet, increment){
	var td = objet.parentNode;
	var tr = td.parentNode;
	var prix_ht = new Number(tr.getElementsByTagName('span')[0].innerHTML);
	var tva = new Number(document.getElementById("selection_tva").innerHTML);
	var total_ht = new Number(document.getElementById("selection_total_ht").innerHTML) + prix_ht * increment;

	td.getElementsByTagName('input')[0].value = new Number(td.getElementsByTagName('input')[0].value) + increment;
	
  document.getElementById("selection_total_ht").innerHTML = total_ht;
  document.getElementById("selection_prix_tva").innerHTML = Math.round(total_ht * tva) / 100;
  document.getElementById("selection_total_ttc").innerHTML = Math.round(total_ht * (1 + tva / 100) * 100) / 100;
}