I was having an issue where due to performance reasons I created a corteza module with a direct table mapping (not using json, mapping to colums).
This made the bulk insert of records much faster, however, values were being rounded up to nearest whole number.
Not sure if this happened because I created the table and did not select right precision, but the fix was easy.
Enter the database and change the numeric field type from (3,0) to (5,2) or whatever precision you need. Then inserts from corteza will maintain the right precision.
I am using postgres so used pgadmin.