Yes. A purchase is converted at the official reference rate of the day it was bought, and the disposal at the rate of the day it was sold, which is how the realised gain and the cost behind it are worked out.
This is where hand-built spreadsheets usually go wrong. Converting a whole year at one rate can move a gain by more than the gain itself when the currency has run.
Rates come from the published daily series, so the same trade converts the same way every time you open the report.
See the tax report