I have been scouring the web trying to find out why there is a difference in
the way Excel does some rounding.

I am using this formula:
=ROUNDUP(IF(A1B1,(B1+1-A1)*96,(B1-A1)*96),15)

I have it pasted to three sets of cells (C1, C2, C3)

My data is:
A1 = 11:00
A2 = 12:30

B1 = 23:00
B2 = 00:30

C1 = 10:00
C2 = 11:30

Cells A1, A2, B1, B2, C1, C2 have the format of hh:mm.

Cells C1, C2, C3 display the value out to 18 decimal places.

In each situation we have 1 hour and 30 minutes of difference. But the
value shown in the cells a
C1 = 6.000000000000010000
C2 = 5.999999999999990000
C3 = 6.000000000000000000

Because of this difference in the way the rounding is accomplished the my
larger formula gives different answers.

My full formula is:
=IF(E30="CB", IF(((ROUNDUP(IF(B30C30,(C30+1-B30)*96,(C30-B30)*96),0)/96*24)
<= 0.5), 1,
IF(AND(((ROUNDUP(IF(B30C30,(C30+1-B30)*96,(C30-B30)*96),0)/96*24)<=2),(0.500001<=(ROUNDUP(IF(B30C30,(C30+1-B30)*96,(C30-B30)*96),0)/96*24))),
2,
IF(B30="","",IF(C30="","",ROUNDUP(IF(B30C30,(C30+ 1-B30)*96,(C30-B30)*96),0)/96*24)))),
IF(B30="","",IF(C30="","",ROUNDUP(IF(B30C30,(C30+ 1-B30)*96,(C30-B30)*96),0)/96*24)))

It should show the time interval in a decimal format to two decimal places.

But the above full forulma gives these values:
C1 = 1.75 (incorrect)
C2 = 1.50 (correct)
C3 = 1.50 (correct)

Can you give me an idea how I can do a work around of this problem?