As a filing convenience, and without changing the respective liability of the group members, members of a combined reporting group may annually elect to designate one taxpayer member of the combined group to file a single return in the form and manner prescribed by the department, in lieu of filing their own respective returns, provided that the taxpayer designated to file the single return consents to act as surety with respect to the tax liability of all other taxpayers properly included in the combined report and agrees to act as agent on behalf of those taxpayers for the year of the election for tax matters relating to the combined report for that year. If for any reason the surety is unwilling or unable to perform its responsibilities, tax liability may be assessed against the taxpayer members.