Populate Column Based On Change In Data Of Another Column

I am trying to find a way to populate a column based on the changes in the data of another column...

For example, I want to fill in the code column....so when the customers cost changes, I want a numeric code to populate & change. So for the first 5 lines, the code could be 21, and then when the cost changes to $37.51, want the code to change to 22.

CodeCustomer's Cost
$34.10
$34.10
$34.10
$34.10
$34.10
$37.51
$37.51
$32.50
$32.50
$33.48
$33.48
$34.10
$37.51
$37.51