Cast string to decimal without rounding the decimal part
You don't show the column definition, but it must be similar to

"conversionFactor" decimal(10,2)


At any rate, the scale of the column must be 2, so PostgreSQL has to round the number to be able to sore it in that column.

You will have to use ALTER TABLE to change the colum definition to be able to store more fractional digits in the column.