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	$11.72	10.257%	$12.9221	$12.92	$12.90	$12.90
Purchase #2	$179.93	4.646%	$188.2895	$188.29	$188.30	$188.30
Purchase #3	$247.86	8.364%	$268.591	$268.59	$268.60	$268.60
Purchase #4	$172.56	6.780%	$184.2596	$184.26	$184.25	$184.30
Purchase #5	$29.85	12.116%	$33.4666	$33.47	$33.45	$33.50
Purchase #6	$21.61	6.720%	$23.0622	$23.06	$23.05	$23.10
Purchase #7	$114.25	8.417%	$123.8664	$123.87	$123.85	$123.90
7 purchase totals =	$777.78		$834.4574	$834.46	$834.40	$834.60