The six T-shirts cost 6 x $8 = $<<6*8=48>>48.
The four sweaters cost 4 x $18 = $<<4*18=72>>72.
And five jackets normally cost 5 x $80 = $<<5*80=400>>400.
So, a discount of 10/100 x $400 = $<<10/100*400=40>>40 for the five jackets.
Thus, the selling price of the five jackets is $400 - $40 = $<<400-40=360>>360.
Hence, the total cost of all the items is $48 + $72 + $360 = $<<48+72+360=480>>480.
The sales tax is equal to 5/100 x $480 = $<<5/100*480=24>>24.
Therefore, Kevin has to pay $480 + $24 = $<<480+24=504>>504. including the sales tax.
#### 504