The popularity of digital music, videos and e-books has exploded in the past decade as consumers migrate to the Web. Merchants have been reluctant to accept credit cards for some of these items, which sell for as low as 79 cents, because fees make up a high percentage of the value of the transaction, reducing profit. Changing the fee structure will allow merchants to sell these goods more profitably, Rovetta said.  PayPal’s standard fee for processing a transaction is about 3 percent of the transaction plus a flat rate of 30 cents. For purchases less than $10, it charges 5 percent plus 5 cents.  That means when a consumer buys a 99-cent song online, the merchant would pay PayPal about 10 cents, or 10 percent of the transaction. Under the aggregation model, PayPal wouldn’t charge the merchant until consumers bought, say, 10 or 20 songs, thereby reducing the percentage of the transaction the merchant is charged.