MySQL error 1066 - Error Code: 1066. Not unique table/alias: 'TAXES'
Because you have 2 times TAXES in your FROM clause (here between **):

FROM TICKETLINES
INNER JOIN PRODUCTS_CAT ON PRODUCTS.ID=PRODUCTS_CAT.PRODUCT
JOIN TAXCATEGORIES ON PPRODUCTS.TAXCAT=TAXCATEGORIES.ID
JOIN **TAXES** ON TAXCATEGORIES.ID=TAXES.ID
LEFT OUTER JOIN PRODUCTS ON TICKETLINES.PRODUCT=PRODUCTS.ID
LEFT OUTER JOIN TICKETS ON TICKETS.ID=TICKETLINES.TICKET
LEFT OUTER JOIN RECEIPTS ON RECEIPTS.ID=TICKETS.ID, **TAXES**