A great way to earn a few bucks is to take advantage of category bonuses on Chase Freedom, Discover It, and Citi and buy $500 VGC and burn them on taxes. These are debit payments and the cost is around $2-$3 per card unloaded. You can do $3,000 per estimated tax period and $3,000 for an extension (form 4868) for a total of $15,000 unloaded this way; more if you call in to Official Payments and unload multiple cards in one transaction. You are limited to two payments per processor, so six total. I underwithhold my taxes at work and pay estimated taxes for this reason, although not to the $15,000 max. The same goes for the Simon $1,000 cards, which can be unloaded this way but don’t provide category bonuses.
Paypal also takes taxes from PayUSATax and so when the Paypal category rolls around, that’s an easy way to get a 3% delta on tax payments. Also, taxes on credit card signups. Even with the base fee, it is slightly cheaper to unload $500 cards on taxes than to pay taxes directly (a fee of $8.95 - $6.95 for the card and $2 to unload, compared to $9.45 when a $500 payment is directly made) but I save unloading for grocery store promos. I used to unload office store Mastercards on Plastiq but that is gone in eight days.