Despite the attention that Amazon’s technology receives — its latest e-readers were introduced last week to the usual fanfare — the majority of its sales are old-fashioned three-dimensional objects. The company’s retail sales in the United States are on track this year to be roughly comparable to those of enterprises like McDonald’s, Sears and Safeway. And while its sales are only about 12 percent that of Walmart, the reigning retail kingpin, they are increasing much faster.

“Amazon is the giant sucking sound in retail,” said Colin Gillis, an analyst at BGC Partners. But the company, he added, is switching to an untested game plan: “They have to hope that same-day delivery will offset the price advantage they no longer have.”

Since the company’s founding, Mr. Bezos held on tightly to a 1992 Supreme Court decision that said mail-order merchants did not have to collect tax in states where they did not have physical operations. (Consumers were supposed to pay a use tax directly to the state, but few did.)

“The original justification for this de facto tax exemption was that the Internet ought to get some growing space,” said Michael Mazerov, a senior fellow at the Center on Budget and Policy Priorities. “Amazon collecting the tax in California, the birthplace of the commercial Internet, says that the Net can compete on a level playing field with traditional retail.”

Amazon executives maintained that the sales tax exemption was not much of an advantage. Its regulatory filings told a different story, noting that collecting taxes could “decrease our ability to compete.”

California retailers, particularly a handful of remaining independent booksellers, would love to see a dent in Amazon’s business. “Oliver Wendell Holmes said taxes are the price of civilization, but Amazon did not want to pay,” said Michael Barnard, president of the Northern California Independent Booksellers Association.

Booksellers concede that Amazon, which offers a flat annual rate for fast shipping to encourage frequent orders, is still likely to be cheaper even when it collects taxes. The most Mr. Barnard can hope is that Amazon’s notoriously low margins — it makes little more than a penny for every dollar in sales — will eventually catch up with it. “Same-day delivery is very, very expensive,” he said.