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	$84.26	6.485%	$89.7243	$89.72	$89.70	$89.70
Purchase #2	$227.47	10.168%	$250.5991	$250.60	$250.60	$250.60
Purchase #3	$122.32	10.341%	$134.9691	$134.97	$134.95	$135.00
Purchase #4	$49.82	7.623%	$53.6178	$53.62	$53.60	$53.60
Purchase #5	$122.57	3.729%	$127.1406	$127.14	$127.15	$127.10
Purchase #6	$151.46	7.658%	$163.0588	$163.06	$163.05	$163.10
Purchase #7	$140.45	13.143%	$158.9093	$158.91	$158.90	$158.90
7 purchase totals =	$898.35		$978.0190	$978.02	$977.95	$978.00