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	$162.62	10.719%	$180.0512	$180.05	$180.05	$180.10
Purchase #2	$162.74	6.158%	$172.7615	$172.76	$172.75	$172.80
Purchase #3	$20.64	7.605%	$22.2097	$22.21	$22.20	$22.20
Purchase #4	$117.72	8.395%	$127.6026	$127.60	$127.60	$127.60
Purchase #5	$48.39	9.302%	$52.8912	$52.89	$52.90	$52.90
Purchase #6	$238.45	4.414%	$248.9752	$248.98	$249.00	$249.00
Purchase #7	$31.66	13.174%	$35.8309	$35.83	$35.85	$35.80
7 purchase totals =	$782.22		$840.3223	$840.32	$840.35	$840.40