Each individual hit gets a boost.
It doesn't matter if the overall base power goes above 60, if the original base power is below 60, then it receives the Technician boost.
So for example, the base power of Bullet Seed is 25, so each consecutive hit receives a boost from Technician.
This applies to all multi-strike moves such as Rock Blast, it's the reason Technician Breloom is so popular.