If you bind a limit to your fetching request (axios.get(...&_limit=10)), you can't return a paginate count because your computed evenPost property will always return 1 i.e Math.ceil(10/10) == 1

To fix your pagination, remove the parameters query to get the data:

getData() {
  axios.get('https://jsonplaceholder.typicode.com/posts').then(response => {
    this.posts = response.data
  })
}

Then change the default counter page to 0 and add a computed property to return 10 posts based on it:

data () {
  return {
    counter: 0,
    //...
  }
},
computed: {
   paginatedPosts() {
    const start = this.counter * 10;
    const end = start + 10;
    return this.posts.slice(start, end);
  }
}

Now you can iterate on this property:

<ul>
  <li v-for="(post, index) of paginatedPosts" class="post">
    ...
  </li>
</ul>

Basic live example

You can do that dynamicly on the server, by creating some html files each represents a page and each contains 10 items of your data, or you can do some tricks with JavaScript on client side, by dividing your html into sets each set groups 10 items of your data, and hide all the sets except for the first one, and create some buttons for the user to simulate pagination, previous and next, when the user clicks next you need to hide all of the sets and show the second one, and build you logic...