Loss of decimal precision when invoice is saved in database

The "Unit Price" loses precision when it is saved in db.

## Steps to reproduce
- Create a new invoice
- Create an invoice item
- Set any decimal number with 3 places as unit price(example: `0.141`)
- Save the invoice
- Reload the page
- Unit price is `0.14`


## Expected result
- The unit price stays `0.141`