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	$162.31	6.292%	$172.5225	$172.52	$172.50	$172.50
Purchase #2	$52.59	12.271%	$59.0433	$59.04	$59.05	$59.00
Purchase #3	$176.65	10.126%	$194.5376	$194.54	$194.55	$194.50
Purchase #4	$184.85	11.374%	$205.8748	$205.87	$205.85	$205.90
Purchase #5	$87.78	13.492%	$99.6233	$99.62	$99.60	$99.60
Purchase #6	$158.82	10.186%	$174.9974	$175.00	$175.00	$175.00
Purchase #7	$18.78	10.786%	$20.8056	$20.81	$20.80	$20.80
7 purchase totals =	$841.78		$927.4045	$927.40	$927.35	$927.30