table {
                border-collapse: collapse;
            }

            /*PARA LA PRIMERA FILA TIENES DOS OPCIONES*/

            tr:first-child td:first-child {
                border-top-left-radius: 10px;
            }

            tr:first-child td:last-child {
                border-top-right-radius: 10px;
            }

            tr:first-child td:only-child {
                border-top-right-radius: 10px;
                border-top-left-radius: 10px;
            }

            /*si en lugar de eso has usado la etiquetas thead y th es más
sencillo todavía*/

            th:first-child {
                border-top-left-radius: 10px;
            }

            th:last-child {
                border-top-right-radius: 10px;
            }

            th:only-child {
                border-top-right-radius: 10px;
                border-top-left-radius: 10px;
            }

            /*Y ASÍ PONEMOS EL PIE*/

            tr:last-child td:first-child {
                border-bottom-left-radius: 10px;
            }

            tr:last-child td:last-child {
                border-bottom-right-radius: 10px;
            }

            tr:last-child td:only-child {
                border-bottom-right-radius: 10px;
                border-bottom-left-radius: 10px;
            }