10
Tom never bought his own sweets in Honeydukes; he hoarded the money he was given by the school for his equipment, always careful to spread it out, rather than risk running short. Besides, he didn't need to. Other people bought them for him.
Some was as thanks, for help with a piece of work, for smoothing something over with a teacher, covering up for something. It was best to pay off that kind of debt quickly, because if left, it could be called in when you least expected it. Tom was careful to never need that kind of help. He only gave it.
Some was bribery, really, trying to get on his good side. Rumours abounded that he was descended from Slytherin himself. True rumours, he was certain of it, though he was still desperately hunting for more proof. Proof for himself, though, not for others. Parseltongue was enough for his housemates
Some was paying off, to amend for annoying him. A first year who'd knocked ink over one of his essays, a third year whose cat had left fur and a dead mouse on his bed – they'd pick something up, either from Hogsmede if they were old enough to go, or by owl if they couldn't. Subtly, of course, although admittedly in varying degrees. Some would hand it to him as they walked past, some would owl it to him (he liked that, because he could pretend for a moment that it was someone else, someone outside Hogwarts, sending him something.)
In fact, the only thing Tom himself bought was the odd box of crystallised pineapple. It had taken him less than a term to discover the potion master's favourite treat, and he was careful to occasionally supply a box – at suitable times, of course. Slughorn was so easy to impress, to trick and manipulate. A little flattery, a dose of awe and respect, a small gift. And he was putty. Easy.