one of the banks i dump at will sell me bags of halves (i don't buy 'em because the majority, if not all, are my junkiron), quarters or dimes but won't guarantee the accuracy of the count. seems to me that after they fill the bag they could run the coin again just to be sure of the amount in the sack but....alas, no. they just ship it off to the fed and the fed sends back the total after they run it.
also, one of the machines i dump into can be set to "fill" at different levels. the half dollars used to be set at $800.00 until i showed up and started filling it. they quickly reset it to "fill" at $400.00 because of the weights involved.
so buying sacks of coin may produce some silver or other keepers but you stand the chance of losing some cash due to the inaccuracy of the machines. just a thought.