McGoldrick netted his third goal of the season in the victory at Portman Road, while Daryl Murphy continued his fine start to the campaign when he fired in his side's opener in the clash.
McCarthy told Sky Sports News: "McGoldrick is arguably one of the best strikers in the league. He has two good feet, just one better than the other, and it was some strike.
"September has gone particularly well. We have had a nice bit of momentum, although we have carried a bit of luck.
"It was a fantastic first half for us, although Rotherham were excellent after that and got on the front foot. I will have to analysis that tomorrow."
Ipswich are currently fourth in the Championship after nine matches this season.