Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$13.47	13.789%	$15.3274	$15.33	$15.35	$15.30
Purchase #2	$97.27	8.397%	$105.4378	$105.44	$105.45	$105.40
Purchase #3	$123.44	12.184%	$138.4799	$138.48	$138.50	$138.50
Purchase #4	$158.99	8.735%	$172.8778	$172.88	$172.90	$172.90
Purchase #5	$117.89	8.300%	$127.6749	$127.67	$127.65	$127.70
Purchase #6	$176.72	3.103%	$182.2036	$182.20	$182.20	$182.20
Purchase #7	$61.29	8.574%	$66.545	$66.55	$66.55	$66.50
7 purchase totals =	$749.07		$808.5464	$808.55	$808.60	$808.50