Note that since Aug 2019 the spatial resolution of Tropomi is 5.5x3.5km.
The resolution also depends on the product type. NO2 uses the ‘native’ resolution of the instrument, but for e.g. CO several pixels are combined and the resolution is halved in each dimension.
The resolution of 0.02 degree is a good resolution to use (for e.g. NO2). It slightly oversamples the native resolution of Tropomi itself. It is also the resolution that is used by the S5P Mapping Portal (this uses 2^14 pixels for 360 degrees longitude, which is ~0.022). For CO you would use about 0.04 degree.