I haven't used BTC in a long time but last I read transactions take a very long time to process because the blocksize is too small to contain all the transactions that took place. I read (not sure if this is correct) that transaction fees needed to be upwards of $20 to ensure the transaction was included in the next block.
Bitcoin transactions have something like a $5 average transaction fee. You can offer less but your transaction won't get processed as quickly. Bitcoin is already slow at processing transactions.
Disclaimer: I don't use bitcoin. The $5 number is outdated, but from the graphs I could find in a quick search it seemed to be rising consistently.
I never spend more than $0.10 on transaction fees for bitcoin. I mean, you could give $5 if you wanted to, but why would you?
If I was sending a dollar I wouldn't pay more than $0.01 or less for the transaction fee. And for something so cheap the merchant shouldn't bother waiting on confirmations. Exploiting 0 confirmations isn't easy, and it's not worth the work to anyone for a dollar. Even with sub cent transaction fees they'll still settle faster than 3-5 business days.
Smallest transaction I've seen is 191 bytes; [1] says right now to get a transaction in the next block the minimum fee is 240 satoshis/byte; and that today the 251-260 satoshis/byte has been the most common fee.
That's $2.82 according to [2].
And that's with current levels of demand - if there was a transaction every time someone visited a website, demand would be much, much higher.
That's why you would use an off-chain solution like lightning payment channels with sub-cent transaction fees. Transactions are faster than credit cards too.