For a purely visual aid you could use a custom entry in the turn order and just increment the value each time, or set it as a +1 increment and use the 'next turn' button to do it for you. If you use /r or /roll to make the actual roll you'll also get dice in the chat that you can drag/drop onto the VTT and line up nicely as a visual aid. Third option is to have a token on the page and use either the bubbles to track the number of rolls made or status icons with numbers for a non-selected view on the token. Fourth, create a rollable table with a HUGE number as each side of it and choose the appropriate side after each roll to have a glaring, in your face, reminder. Fifth, train a small, friendly, animal to respond to a simple keyword which would then ring a bell a number of times equal to the rolls made... you'd need to train it to reset the count occasionally too so not 100% that is your best option here, but possibly the most fun one!