If you saved your receipts throughout the year, you can add up the
total amount of sales taxes you actually paid and claim that amount. If you didn't save your receipts, you can fill out the worksheet and use the optional general sales tax tables in the instructions for federal Schedule A (Form 1040) or use the Sales Tax Deduction Calculator available on the Internal Revenue Service's website.
If you claimed your state income taxes as an itemized deduction on your federal return, you cannot claim the deduction for sales taxes on your Montana return. Also, none of the resort, accommodations or similar taxes collected in Montana qualify as a general sales tax under the federal definitions, so they cannot be deducted.