Currently Kashoo does not have any specific support for sub-accounts. However, our users have had some success with two ways around this:
Use a common prefix on the names of grouped accounts; for example "Travel - Meals" and "Travel - Car Rentals". This places the accounts close to one another on the reports.
Use a common prefix on the numbers of grouped accounts and sort them by going to the User Account page in your Settings. Select the "Accounts ordered by Number" setting to sort accounts by number instead of name, and you can then change the numbers of your accounts to similar ones, such as "4001.01", "4001.02", and so on.