JSFiddle - React, Tailwind, and code Playground

HTML

<span class="desconto-de vtex-cpSave vtex-cpShow ">15,0 % OFF</span>

<span class="desconto-de vtex-cpSave vtex-cpShow ">25,20 % OFF</span>

<span class="desconto-de vtex-cpSave vtex-cpShow ">35,30 % OFF</span>

<span class="desconto-de vtex-cpSave vtex-cpShow ">45,70 % OFF</span>

CSS

span {
    width: 100%;
    float: left;
}

JavaScript

function limparClasse(classe) {
    var elementos = document.querySelectorAll('.' + classe);
    for (var i = 0; i < elementos.length; i++) {
        var elemento = elementos[i];
        var string = elemento.innerHTML;
        var novaString = string.split('%');
        var arredondamento = parseInt(novaString[0], 10);
        var resultado = arredondamento + '%' + novaString[1];
        elemento.innerHTML = resultado;
    }
}


limparClasse('vtex-cpShow');