Wales' hopes of booking a first World Cup final appearance died with an agonising 9-8 defeat against France last weekend.
They now have the consolation target of a third-place finish, though, which would equal their best World Cup performance 24 years ago.
And centre Roberts said: "We are a very dedicated group of guys - we are very passionate.
"You wear the Wales shirt and regardless of the occasion, you give it your all. We will certainly be giving it our all on Friday.
"We want to end the tournament on a high. It would be disappointing to lose to Australia and go home having lost two games (in a row), so we certainly want to win."
One of the tournament's great potential match-ups will not happen on Friday after Wales captain Sam Warburton's red card against France and subsequent three-week ban ended his competition.
And that has ruled out a battle with revered Australian openside flanker David Pocock.
"I think it's a great shame we don't get to see Pocock take on Warburton," Roberts added.
"That would have been an incredible battle to watch. Sam has proved that he's up with the best in the world in this tournament."
Roger Lewis, meanwhile, believes Wales' World Cup heroes have launched "a golden era" for Welsh rugby with their eye-catching exploits in New Zealand.
Coach Warren Gatland is under contract until 2015, while a deal was struck earlier this year with the players to 2016.
"It truly is an exciting period," Welsh Rugby Union group chief executive Lewis said.
"This is most probably the first golden era of Welsh rugby in the professional era.
"This tournament has been an absolutely resounding success for Welsh rugby.
"It has given us all a great deal of confidence, it has given us all a greater pride, it has given us a sense that we have such an exciting future ahead of us."
More than 60,000 people watched Wales face France on giant screens at the Millennium Stadium, and Lewis confirmed the exercise would be repeated for Friday's third-place clash.
"The energy that has been created by this group of players, it's so powerful that we have now got to harness it and drive the game forward in Wales," he added.
"The next four years is going to be so exciting for this coaching team and this group of players.
"After what they have achieved here and all the hard work they have put in over the last few years, they have now got it all ahead of them."
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