Hi nokia77,
an exchange between different grids and/or SL was never taken into consideration while developing the module

and there is no intention from my side to do so.
But the tables you are looking for are (replace #__ with your Joomla db prefix):
#__opensim_moneybalances (for the balances of users)
#__opensim_moneytransactions (for single transaction details)
Greetz
FoTo50