Sales Tax is calculated based on individual tickets, not entire orders. Here's an example:

On a $10 ticket we round from $0.675 to $0.68

And on a $5 ticket we round up from $0.3375 to $0.34

So an order with two $10 tickets is $0.68 + $0.68 = $1.36 and not $1.35 as you might expect when doing $20 * 6.75