Hi there,
I dont know how many agree with me, but I feel that the microcontroller should not be used to drive loads or sink large amounts of current. The Micro should to be used as the embedded
core of one's system and used only to analyize inputs and based on the control algorithm provide the appropriate output signals!

These output signals (low current) should be used as inputs to driver elements such as BJTs, FETs, Open collector driver gates, etc.

In this way the micro is never in a position where it has to handle too much current that may cause damage to the device.
In your case, it is all well and good the each pin can sink 20mA,
but you have to consider how many LEDs you are driving. How much current can a port sink when all the pins are driving LEDs? Your data sheet may show that all 8 LEDs may not be driven by a single port. Also, all Micro cannot sink such currents, and you may overlook this in the future. So, it might be a good idea and also a good design practice to use a driver from now.

The only reason that it might not me a good idea to use drivers in your case is, if you plan to build thousands of your designs, in that case the cost factor may come into play.

I hope this helps.
All the best,
sun.