You can (and should) upvote even below 0.02.

There are two different dust numbers. One is at roughly 0.001, and every vote is 'taxed' by that amount. The second is at payout. A post must have more than 0.02 to get payment. As long as it has at least 0.02 when all vote values are added together, then it will get paid.

So you shouldn't vote less than 0.02 on anything that doesn't already have 0.02, unless your vote will push it over. Then you should anyway. There is also a service called @dustsweeper that I use on my account and all SBI accounts. It will upvote any comments that already have an upvote by enough to push payout above 0.02. That way no smaller upvotes that we receive are ever wasted.

Edit: I deliberately upvoted your comment below 0.02. I'll come through later and upvote all the comments that actually add something to the discussion with an SBI account (this is pretty standard practice for SBI, actually). The total we be above 0.02 and your comment will get paid. You will be able to see that my upvote still contributes to the total payout of your comment, even though it was below 0.02.