Well a dime coin is .10cents, and a nickel coin is .5cents, sooooo, a "dimebag" means $10 worth, and a "nickel bag" is $5 worth.

$5 worth is generally a joints worth, a standard size joint, so $10 worth would be double that.

That's how it was for back in the day us anyways, where you could actually buy bags that small.