my recommendation would be to redefine the structure of your xml so that it is not using a different tag name for every record. however, that may not be possible depending on your situation.
the current structure of your xml will never work to effectively report or chart off of unless you always have 10 temps and 10 pressures in each xml file. otherwise the number of fields being brought in changes.
however, if you always have 10 temps and 10 pressures then please see the blog post here regarding rolling up records and passing them to a subreport.
in your case you would roll up the records in 2 formulae, one named temp and the other pressure. syntax for rolling up temp would be:
{Tag.TEMP1} + '^' + {Tag.TEMP2} + '^' + ...etc.
in the blog post there is a sample report.
good luck,
jamie