Hello, 

When the store attribute is equal to True it needs it will be stored in the database. When stored is equal to False the computed field is calculated on the fly. So when stored is False you will see the value as the record loads into the view. 

When store is True you need to change the fields in the depends decorator to see a change in the field. Sof to this example: 

from odoo import api
total = fields.Float(compute='_compute_total', store=True)
@api.depends('value', 'tax')
def _compute_total(self):
    for record in self:
        record.total = record.value + record.value * record.tax

Only when the fields "value" or "tax" are changed your field will display the correct value. I would suggest doing a mass update of the fields that depend on your computed field. 

I hope this helps,