ATUM uses multiple custom tables to store the data. If you take a look at your database, all those starting by atum prefix, are the ATUM's custom tables.
- atum_product_data (here is the purchase price amongst others)
- atum_inventories (here are saved the multi-inventories with their main properties)
- atum_inventory_locations (here are saved the relationships for the multi-inventory locations)
- atum_inventory_meta (here are stored the meta props for multi-inventories)
- atum_inventory_orders (here you'll find the multi-inventory information for order items)
- atum_inventory_regions (here are stored the relationships for the multi-inventory zones when shipping restriction mode is enabled)
Hope this helps.