For example, in the UK VAT is 17.5%, so you make a new column in Excel (or OpenOffice calc) and in B2 you put =A1*1.1.75 (assuming your prices are in column A) and copy down the column.
If you want to copy back the VAT-inclusive prices, just select them all, then paste-special, and you want just values (otherwise you'll have a circular reference)
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