As you know, financial types can either be deductible or non-deductible. Before the advent of price sets, to record a partially deductible contribution you would use a deductible financial type and then enter in the non-deductible amount. After the advent of price sets, if the overall financial type of a price set is non-deductible, the system will automatically populate the non-deductible amount field for the full amount of the contribution, regardless of whether the individual price field options are configured with deductible financial types.
What this means is that currently, the system only tracks a non-deductible amount on the contribution level, not on the line item level. The field in the line item table is either a legacy field or a place holder for future use, but it is not something that is currently being populated by the system.
The demo site is down so I am unable to verify what built in tax tokens are available, but for our clients we instruct them to use a deductible financial type for the price set - in this way, our line-item based tokens will allocate each line item's deductible amount according to the financial type of the price field option.
Hope this helps,