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	$12.64	7.604%	$13.6011	$13.60	$13.60	$13.60
Purchase #2	$153.99	6.317%	$163.7175	$163.72	$163.70	$163.70
Purchase #3	$145.70	3.308%	$150.5198	$150.52	$150.50	$150.50
Purchase #4	$115.47	10.637%	$127.7525	$127.75	$127.75	$127.80
Purchase #5	$173.25	10.685%	$191.7618	$191.76	$191.75	$191.80
Purchase #6	$103.65	4.314%	$108.1215	$108.12	$108.10	$108.10
Purchase #7	$79.90	13.546%	$90.7233	$90.72	$90.70	$90.70
7 purchase totals =	$784.60		$846.1975	$846.19	$846.10	$846.20