Sharp XE-A102 - till roll printing lots of junk info?

Our Sharp XE-A102 cash register has started printing lots of junk out when we process transactions.

We get lots of lines of dots mid transaction. Sometimes the transaction doesn't appear to process properly eg we'll type in one figure and the department code and it will print out on the till roll, you type in the next figure and the department code and it reprints the first one again. When you subtotal the amount is correct but we end up with these erroneous entries being printed out.

It used to only happen on the first couple of transactions in the morning. Now it is happening all the time - it takes ages to process the transction and is using up lots of paper!

Any ideas?