Follow these steps:

1. For the Label value in the Pivot - Values - General tab enter this expression:
=FORMAT(SUM(Fields!MyField), "C")
this expression will format the label of the data point to show as currency.

2. For the Format value in the Pivot - Values - Data Labels tab enter this expression:
<label>
this instructs the chart to show only the label for each data point.

Hope this helps - questions or comments - please feel free.