Customize menu --> ArcMap Options --> Sharing tab
Under the Packaging section, tick the ‘Enable ArcGIS Runtime Tools’
- File Menu --> Share As --> Tile Package.
You can choose to directly push it to your ArcGIS Online account (would need to be signed in first) from ArcMap, or you can create it as a file and then upload it via ArcGIS Online --> My Content.
However, if you expect the tile package to be over 256mb, recommend creating locally and then using the Share Package Tool under Data Management Toolbox.
Once uploaded, you then need to publish - this unpacks the tiles into a tiled map service (a new item) and voila.
You can check the status of the unpacking/publishing from the item page for the new tiled map service.
This is a handy way to bypass using up credits for creating caches, but remember you also use credits for storage of tiles, therefore worth deleting the original tile package item, as you no longer need this.