Amazon's (AMZN) giant annual Prime Day sale is here, and by now it's practically synonymous for bargains in online shopping. But does the e-commerce juggernaut always have the best deals? That depends.

According to an analysis done for CBS MoneyWatch by retail technology firm Boomerang Commerce, of the 100 top-selling toys and games, electronics, and home and kitchen products on Amazon, the Seattle-based company enjoys an advantage over its closest rival Walmart (WMT). Boomerang found that Walmart's prices are on average 35 percent higher than Amazon's in toys and games and 20 percent more in home and kitchen.

Target (TGT) is 2 percent more expensive than Amazon in toys and games and 11 percent higher in home and kitchen, according to Boomerang.

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When it comes to electronics, all three were nearly even when it comes to price. Target is 5 percent is more expensive in electronics than Amazon, while Best Buy (BBY) was on average 2 percent higher. Walmart was on average 3 percent less than Amazon. On big-ticket items like consumer electronics, retailers often will match rivals' prices.

"If you're a shopper buying a pretty common item, on average Amazon is still going to be the cheapest. But if you're buying something that's a lot more niche, then you might need to shop around," said Michelle Ai, marketing manager at Boomerang.

Some of the disparity in prices between Amazon and its rivals can be explained by the numbers of products independent retailers sell on the site. But even when those sales are stripped away, Amazon's prices remain competitive, according to Ai. Target and Best Buy don't use third-party sellers on their sites.

Officials from Amazon declined comment for this story. Walmart had no immediate comment. Target's pricing approach includes offering "compelling promotions year-round based on our guests' shopping mindset," said spokesman Eddie Baeb.

For Prime Day, Amazon is offering steep discounts on electronics such as its Amazon Echo smart speaker and the Fire tablet. The Echo is priced at $89.99, a 50 percent discount.

According to BestBlackFriday.com, that's $50 lower than what it sold for on Black Friday 2016 and $40 cheaper than last year's Prime Day. The Amazon Echo Dot ($34.99), Kindle Paperwhite ($89.99) and the all-New Fire 7 tablet ($29.99) are also cheaper than they were on last Prime Day and Black Friday.

BestBlackFriday estimates that 77 percent of 2017 Prime Day prices are better than Black Friday, with 12.9 percent being tied.

"You'll find some great deals and low prices, but also do your research since several other retailers are also hosting sales now to compete with Amazon. So you could find it for less elsewhere," according to Sara Skirboll of RetailMeNot.

Amazon's rivals are indeed trying to steal the Seattle-based company's thunder on its big day. Walmart is advertising "huge" summer savings on its website, including up to $30 off on select products made by Google (GOOG), such as the Google Home smart speaker. Target is aiming at back-to-school online shoppers by touting that it offers everything needed from "K [kindergarten] to Ph.D." Best Buy is promising "deals in every department."

Amazon Prime Day last year was the company's single biggest sales day ever. Buoyed by the success, Amazon has expanded the self-created holiday by 25 percent to 30 hours, most likely setting the stage for another record performance.