Rounding To The Nearest 5 (VB Code)

In cell A1, I might have the following numbers: 1, 5, 10, 50, 100.
In cell B1, I will have an unknown number
In cell C1, I want to round the number in B1 using the information given in A1.

For example:
A1 = 1
B1 = 153.45
C1 should be 153
C1 = round(B1,0)

A1 = 5
B1 = 153.45
C1 should be 155
C1 = round(B1,0) +/- 5 (depending on the situation)

A1 = 10
B1 = 153.45
C1 should be 150
C1 = round(B1,-1)

A1 = 50
B1 = 153.45
C1 should be 150
C1 = round(B1,-1) +/- 50 (depending on the situation)

Is there a quick of doing this using VB? I can do a bunch of if then statements... but was wondering if there's an easier way.