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	$162.78	5.666%	$172.0031	$172.00	$172.00	$172.00
Purchase #2	$67.55	10.332%	$74.5293	$74.53	$74.55	$74.50
Purchase #3	$58.69	4.762%	$61.4848	$61.48	$61.50	$61.50
Purchase #4	$29.32	9.602%	$32.1353	$32.14	$32.15	$32.10
Purchase #5	$69.79	11.296%	$77.6735	$77.67	$77.65	$77.70
Purchase #6	$112.66	13.529%	$127.9018	$127.90	$127.90	$127.90
Purchase #7	$241.42	4.195%	$251.5476	$251.55	$251.55	$251.50
7 purchase totals =	$742.21		$797.2754	$797.27	$797.30	$797.20