i suggest for tabs to be grouped under one main group Like:-
1- Customers Tabs:- (Customers ; sales quotes ; sales orders ; sales invoices ; credit notes)
and the same for supplies tabs , inventory tabs , fixed assets tabs , bank and cash accounts.
Group similar tabs into one main tab that can expand and shrink by clicking the mouse.)
Please read the closed discussion at Manager Navigation Feedback
They actually are already grouped that way. There are just no headings like those you suggest. That is because almost all tabs are optional. Many businesses use only one or even no tabs in a group, so headings would just consume lots of screen space, requiring more scrolling, which is one of the most frequent complaints about the interface already.