if you want the rounded corners to be those of the header line and those of the last line, use this code
.wpsm-thead th:first-child {-webkit-border-top-left-radius: 20px; -moz-border-radius-topleft: 20px; border-top-left-radius: 20px;}
.wpsm-thead th:last-child {-webkit-border-top-right-radius: 20px; -moz-border-radius-topright: 20px; border-top-right-radius: 20px;}
.wpsm-comptable tr:last-child td:first-child{-webkit-border-bottom-left-radius: 20px;; -moz-border-radius-bottomleft: 20px; border-bottom-left-radius: 20px;}
.wpsm-comptable tr:last-child td:last-child{-webkit-border-bottom-right-radius: 20px; -moz-border-radius-bottomright: 20px; border-bottom-right-radius: 20px;}
if you want the rounded corners to be those of the first line and those of the last line, excluding the header line, use this code:
.wpsm-comptable tr:first-child td:first-child {-webkit-border-top-left-radius: 20px; -moz-border-radius-topleft: 20px; border-top-left-radius: 20px;}
.wpsm-comptable tr:first-child td:last-child {-webkit-border-top-right-radius: 20px; -moz-border-radius-topright: 20px; border-top-right-radius: 20px;}
.wpsm-comptable tr:last-child td:first-child{-webkit-border-bottom-left-radius: 20px;; -moz-border-radius-bottomleft: 20px; border-bottom-left-radius: 20px;}
.wpsm-comptable tr:last-child td:last-child{-webkit-border-bottom-right-radius: 20px; -moz-border-radius-bottomright: 20px; border-bottom-right-radius: 20px;}