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	$96.83	3.651%	$100.3653	$100.37	$100.35	$100.40
Purchase #2	$159.48	5.194%	$167.7634	$167.76	$167.75	$167.80
Purchase #3	$167.78	10.578%	$185.5278	$185.53	$185.55	$185.50
Purchase #4	$134.84	6.585%	$143.7192	$143.72	$143.70	$143.70
Purchase #5	$141.81	3.388%	$146.6145	$146.61	$146.60	$146.60
Purchase #6	$46.30	5.400%	$48.8002	$48.80	$48.80	$48.80
Purchase #7	$141.99	5.127%	$149.2698	$149.27	$149.25	$149.30
7 purchase totals =	$889.03		$942.0602	$942.06	$942.00	$942.10