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	$156.49	11.560%	$174.5802	$174.58	$174.60	$174.60
Purchase #2	$55.73	11.676%	$62.237	$62.24	$62.25	$62.20
Purchase #3	$238.32	13.746%	$271.0795	$271.08	$271.10	$271.10
Purchase #4	$10.40	6.645%	$11.0911	$11.09	$11.10	$11.10
Purchase #5	$132.40	5.669%	$139.9058	$139.91	$139.90	$139.90
Purchase #6	$118.34	7.343%	$127.0297	$127.03	$127.05	$127.00
Purchase #7	$91.70	8.823%	$99.7907	$99.79	$99.80	$99.80
7 purchase totals =	$803.38		$885.7140	$885.72	$885.80	$885.70