Whether it’s because you left a dubious tab open on an iPad you just handed to a colleague, or because it’s easier to go through and close a group of tabs from your Mac rather than your iOS device, be aware that since Yosemite you can close any open tab on any device signed in to your Apple ID from Safari.
Here’s how you do it:
On your Mac, click the icon that resembles two overlapping squares in Safari, or choose “Show All Tabs” from the View menu. You’ll see all open tabs on all of your devices. Hover over each and you’ll see a close button you can click should you so desire.
This tip works from iOS to Mac as well; swipe right to left on a cloud tab in its tab view and tap Delete, and that tab will be closed on the Mac.