Depending on your understanding of relational databases, and what you need for your accounting, the micros DB, might not be what you're actually looking for. Azrobert's exactly right (IMO), the data in the micros database can be *difficult* to track down, and what's worse is that it can be *seemingly* contradictory, ie you'll find multiple sets of sales totals for a day, but they won't match, this is especially true if you're writing your own queries.
If you do dive into the DB, I would suggest starting with the daily sales totals. These tables are named dly_xxx_xxx where the x's are the parts of the system, and the items that are being totaled (dly_sys_mi_ttl = daily system menu item totals). These tables seem to be calculated at the end of business dates.
That are far more detailed tables that actually capture the definitions of what make the micros POS work (menu item defs, employee defs, condiment defs, major group defs, etc). There are also tables that capture every detail of a transaction (menu item, seat number, taxes paid, time, etc).
Personally I find the micros database easier to deal with than the software, however I'm familiar with SQL. Also with that being said, I also find the micros database to be 'a work in progress', any more ranting would be OT, but I could go on at great length.