Edit in JSFiddle

<ul class="list">
<!--
  <li class="item">
    <p class="title -compress -ellipsis">あいうえお</p>
  </li>
-->
</ul>

.list {
  display: flex;
  flex-wrap: wrap;
  padding: 10px;
}
.list > .item {
  margin: 10px;
}

.item {
  width: 75px;
  height: 30px;
  box-shadow: 0 1px 3px rgba(0,0,0,.3);
  background-color: white;
}

.item > .title {
  overflow: hidden;
  text-align: center;
  line-height: 30px;
}

.title.-compress {
  letter-spacing: -4px;
}
.title.-ellipsis {
  white-space: nowrap;
  text-overflow: ellipsis;
}

const list = document.getElementsByClassName('list')[0];

const generateTitle = i => {
  const chars = ['あ', 'い', 'う', 'え', 'お'];
  let title = '';
  [...Array(i)].forEach((a, j) => title += chars[j % 5]);
  return title;
};

// テキストの幅を取得
const getTextWidth = text => {
  const span = document.createElement('span');
  span.innerText = text;
  span.style.visibility = 'hidden';
  document.body.appendChild(span);
  
  setTimeout(() => {
    document.body.removeChild(span);
  }, 100);
  
  return span.offsetWidth || 0;
};

const main = () => {
  [...Array(10)].forEach((a, i) => {
    const item = document.createElement('li');
    item.classList.add('item');

    const title = document.createElement('p');
    title.classList.add('title');

    const text = generateTitle(i + 1);
    const width = getTextWidth(text);

    if (80 <= width && width <= 96) {
      // 5〜6文字
      title.classList.add('-compress');
    } else if (96 < width) {
      // 7文字以上
      title.classList.add('-compress', '-ellipsis');
    }

    title.innerText = text;

    item.appendChild(title);
    list.appendChild(item);
  });
};

main();