Generally, each spouse deducts what they actually paid.
The IRS will usually not object if you divide the deductions in some other way for your convenience, but it is important to remember that if you file separately and one spouse itemizes, then both spouses must itemize--if one spouse takes all the deductions, the other spouse must itemize also and take a zero deduction. The other spouse does not get the standard deduction.
Also, you must not claim more than the overall total.
