There are basically two ways to do five cent transactions. The first way is to buy a virtual currency for a non-micropayment amount (e.g. $5 or $25) and then subdivide that virtual currency into infinitely divisible bits which you can spend seemlessly within the application. This is the successful, Zynga-esque way to do micropayments, and it sits nicely atop the legacy payment infrastructure, which is entirely suited to doing $5 or $25 transactions.
The other way, where you attempt to make an actual transaction for $0.05, is an operations nightmare. The legacy payment system is fundamentally not equipped to handle it. The conversion rates to purchases will be terrible, because of the "penny gap" (asking people to spend money, and in particular asking them to make a new relationship to spend money, always causes a huge dropoff) and the conversion rate will not be meaningfully higher than if you had charged $5. Customers hate the experience of authentication for $0.05 transactions even more than they hate actually paying money, and common schemes for doing the auth once and then bundling transactions across merchants like e.g. Flattr are basically a non-starter for most users.
(I'm largely speaking about making services for the global rich here. It is possible that the situation in Uruguay is different, although I'd still suggest not getting into this field as a student.)
