rounded_preds is of shape: [64,10]
y is of shape: [64]
You would have to convert rounded_preds into [64] before you could carry out the operation. You would have to select the index which has the maximum probability value as the predicted class.
Replace
correct = (rounded_preds == y).float()
with
_,pred_label = torch.max(rounded_pred, dim = 1)
correct = (pred_label == y).float()