I found that this was also asked on Reddit. You can try it yourself making a $0.01 market order. There's no fee for this.  It says there's a .005 fee for .20, however if you do it twice you aren't actually charged a fee. On the other side, you cannot sell pennies at a time.  The minimum sell is 0.01BTC (~$80).

I don't think they are trying to buy a $1M a penny at a time though. 8,640 10-second periods a day come to $86.40 and $1,728/day.  If you want to buy without fees and at a better price a post only limit order will do that.  One theory is that this is DCA (https://www.investopedia.com/terms/d/dollarcostaveraging.asp). I think these also could be arbitrage bots testing the market spread.

https://www.reddit.com/r/BitcoinMarkets/comments/73nw0i/a_bot_is_buying_1_cent_of_btc_every_2_seconds_on/