I just discovered that if you purchase a voucher in the shop, then exit out to the main menu without leaving the shop, then continue the run, the voucher will re-appear as if you haven't bought it. However, it will still increase the amount of times you have bought that voucher.
So, if you have enough money to purchase a voucher, you can buy it over and over again through the above method to increase your purchase stat.
This can definitely be used to cheese the anti-matter unlock - likely works for other vouchers as well, though I haven't tested them.
I imagine that it's unintentional, so I figured I'd report it!
Cheers :)