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	$166.78	7.643%	$179.527	$179.53	$179.55	$179.50
Purchase #2	$77.77	11.360%	$86.6047	$86.60	$86.60	$86.60
Purchase #3	$175.85	10.329%	$194.0135	$194.01	$194.00	$194.00
Purchase #4	$239.68	13.301%	$271.5598	$271.56	$271.55	$271.60
Purchase #5	$62.69	6.598%	$66.8263	$66.83	$66.85	$66.80
Purchase #6	$223.84	4.463%	$233.83	$233.83	$233.85	$233.80
Purchase #7	$235.35	9.145%	$256.8728	$256.87	$256.85	$256.90
7 purchase totals =	$1,181.96		$1,289.2341	$1,289.23	$1,289.25	$1,289.20