2010 U.S. online business-to-consumer (B2C) sales totalled $142.5 billion [source]. I couldn't find data for the total number of transactions.
Male/female spending split
Finding annual breakdown of male/female spending in the U.S. is hard, but there's plenty of data to suggest that women purchase more and spend more time online than men do, that they're more 'engaged', and that they research purchase decisions more carefully. From comScore's Women on the Web whitepaper (registration required):
"In the U.S., women are more avid online buyers than men: 12.5 percent of women Internet users made an online purchase in February 2010, compared to 9.3 percent of men. Women’s contribution to e-commerce is greater in terms of buyers, transactions and dollars. In February 2010, for example, they accounted for 49.8 percent of the U.S. online population, but made up 57.9 percent of all non-travel buyers, made 61.1 percent of online purchases and accounted for 58.2 percent of online dollars."
There's much more in the report that might be of interest to you too:
"In the U.S., visiting group-buying sites such as Groupon.com and LivingSocial.com is growing exponentially, and women are driving the growth: females make up 62 and 67 percent of Groupon.com and LivingSocial.com’s U.S. audiences, respectively."
The Nielsen Company's nielsenwire site also suggests that U.S. women shop online more than U.S. men. From their Q3 2010 report:
"Online shopping is popular among both sexes, with almost three-fourths of women (72%) and more than two-thirds of men (68%) having shopped online in the past 30 days. Consumers of both sexes age 35 to 54 had the highest levels of online shopping activity (74%). Women led most online purchase categories except music, auctions and computer hardware."
More from Nielsen, this time on online shopping habits of Moms with kids under 18:
"Moms are more likely to shop for media items: books (11% more likely than the adult online population), magazines (20%), digital music (15%), video games (7%). On the flipside, they tend to shy away from any investment shopping (53% less likely)."