Joint payments.

Married persons may jointly pay estimated taxes unless either spouse is a nonresident alien or the spouses have different taxable years. If they do pay jointly, the provisions under this section applicable to individuals are applicable to the married persons jointly. If a married person files a separate return for a taxable year for which a joint payment was made, the payments may be allocated between themselves as they choose, but if they do not agree on an allocation the department of revenue shall allocate the payments to each spouse on the basis of the ratio of taxes shown on their separate returns or pursuant to default assessment under s. 71.74 (3). If either spouse pays separately, no part of the payment may be allocated to the other spouse.