Convert Time to Decimal with Custom Time Matrix

I am working on a formula to convert flight time into tenths of a decimal but with a catch -there is always a catch, isn't there. The client has specific ranges for which to round up:

:00 - :02 = .0
:03 - :08 = .1
:09 - :14 = .2
:15 - :20 = .3
:21 - :26 = .4
:27 - :32 = .5
:33 - :38 = .6
:39 - :44 = .7
:45 - :50 = .8
:51 - :56 = .9
:57 - 1.02 =1.0

When I put my start time in D5 and finish time in D7, I want the total flight time with the above variables to be displayed in E5. I found some formulas that seemed like they were close, but I can't account for the non-standard rounding - the first group it's two min, the rest are 5 min groups.

Any ideas??