If you're looking for a quick way to view a summary of your sales, on a daily, and monthly basis, you can use the Store Stats page (Members Area > Selling > Store Stats), which provides you with a graph of your daily and monthly sales, for the past month and year respectively, also linked below:
HipStamp Store Stats
HipComic Store Stats
HipPostcard Store Stats
Pro Tip: To view the specific amount for any day or month, hover your mouse over the data points on the chart.
If you're looking for more comprehensive data regarding your sales, please see:
How do I calculate my fees & sales for the year?