If you have a number format that changes for each row in your report this approach keeps the Data item numeric so it can be rendered to a spreadsheet and manipulated as a number.

In the OnRender event for the Data element add a script to modify the data format, i.e.:

var currency = this.getRowData().getColumnValue('Currency');
this.getStyle().numberFormat = currency + "###0.00{RoundingMode=HALF_UP}";

See here for more details.