サンプルHTML
<table class="round-corner" aria-describedby="caption">
<caption id="caption">Table with rounded corners</caption>
<thead>
<tr>
<th scope="col">Head1</th>
<th scope="col">Head2</th>
<th scope="col">Head3</th>
</tr>
</thead>
<tbody>
<tr>
<td scope="rowgroup">tbody1 row1</td>
<td scope="rowgroup">tbody1 row1</td>
<td scope="rowgroup">tbody1 row1</td>
</tr>
<tr>
<td scope="rowgroup">tbody1 row2</td>
<td scope="rowgroup">tbody1 row2</td>
<td scope="rowgroup">tbody1 row2</td>
</tr>
</tbody>
<tbody>
<tr>
<td scope="rowgroup">tbody2 row1</td>
<td scope="rowgroup">tbody2 row1</td>
<td scope="rowgroup">tbody2 row1</td>
</tr>
<tr>
<td scope="rowgroup">tbody2 row2</td>
<td scope="rowgroup">tbody2 row2</td>
<td scope="rowgroup">tbody2 row2</td>
</tr>
</tbody>
<tbody>
<tr>
<td scope="rowgroup">tbody3 row1</td>
<td scope="rowgroup">tbody3 row1</td>
<td scope="rowgroup">tbody3 row1</td>
</tr>
<tr>
<td scope="rowgroup">tbody3 row2</td>
<td scope="rowgroup">tbody3 row2</td>
<td scope="rowgroup">tbody3 row2</td>
</tr>
</tbody>
<tfoot>
<tr>
<td scope="col">Foot</td>
<td scope="col">Foot</td>
<td scope="col">Foot</td>
</tr>
</tfoot>
</table>
簡単にCSSに変換できるSCSSは、sassmeister.comを使用します
table,
th,
td {
border: 1px solid #000;
padding: 8px 12px;
}
.round-corner {
border-collapse: collapse;
border-style: hidden;
box-shadow: 0 0 0 1px #000;
border-radius: 4px;
caption + tbody {
tr:first-child {
td:first-child,
th:first-child {
border-top-left-radius: 4px;
}
td:last-child,
th:last-child {
border-top-right-radius: 4px;
border-right: none;
}
}
}
tbody:first-child {
tr:first-child {
td:first-child,
th:first-child {
border-top-left-radius: 4px;
}
td:last-child,
th:last-child {
border-top-right-radius: 4px;
border-right: none;
}
}
}
tbody:last-child {
tr:last-child {
td:first-child,
th:first-child {
border-bottom-left-radius: 4px;
}
td:last-child,
th:last-child {
border-bottom-right-radius: 4px;
border-right: none;
}
}
}
thead {
tr:last-child {
td:first-child,
th:first-child {
border-top-left-radius: 4px;
}
td:last-child,
th:last-child {
border-top-right-radius: 4px;
border-right: none;
}
}
}
tfoot {
tr:last-child {
td:first-child,
th:first-child {
border-bottom-left-radius: 4px;
}
td:last-child,
th:last-child {
border-bottom-right-radius: 4px;
border-right: none;
}
}
}
table tr th,
table tr td {
border-radius: 0;
}
}
http://jsfiddle.net/MuTLY/xqrgo466/