Дмитрий Ляпунов

var a = 98783.999999999;
a = Math.floor(a);

function Calc5() {
  var discount=+document.getElementById('srok5').value.split('__')[0]
  var sfive=+document.getElementById('srok5').value.split('__')[1] 
  var mfive=+document.getElementById('mesto5').value
  document.getElementById('summ5').value=Math.floor((1-discount/100)*sfive*mfive*8)+' руб.' 
  document.getElementById('dis5').value=discount+'%'	
  document.getElementById('stend').value=mfive+' шт.'
}

function Calc5() {
  var discount=+document.getElementById('srok5').value.split('__')[0]
  var sfive=+document.getElementById('srok5').value.split('__')[1] 
  var mfive=+document.getElementById('mesto5').value
  document.getElementById('summ5').value=Math.round(((1-discount/100)*sfive*mfive*8)/10)*10+' руб.' 
  document.getElementById('dis5').value=discount+'%'	
  document.getElementById('stend').value=mfive+' шт.'
}

The read-only scrollY property of the Window interface returns the number of pixels that the document is currently scrolled vertically

The pageYOffset property is an alias for the scrollY property

An element's scrollTop value is a measurement of the distance from the element's top to its topmost visible content