New custom field capturing total amount of certain line items

Hello Team,

We are trying to achieve a functionality where we create a custom field which takes the sum of total amount of line items.

Let say, we have item type: "Test example" as item 1, item 2, item 3, item 4, item 5.

On creating a sales order, if user selects "test Example" (item 1, item3 and item 5) along with other regular items, We need a custom field which shows the total amount of item 1, item 3 and item 5

Is it possible to achieve?

Thanks

Karan