As with models, there exists different kinds of tags in minecraft and currently digitality can only add item tags. Here's how:
Item tags
data.itemTag("<tag (without the mod id)>","<item1 (with the mod id)>","<item2>"...);
Example
// This code adds the "minecraft:beehives" tag to "minecraft:iron_ingot" and "minecraft:gold_ingot" itemsVirtualDataPack data =newVirtualDataPack("minecraft");data.itemTag("beehives","minecraft:iron_ingot");data.itemTag("beehives","minecraft:gold_ingot");