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	$43.76	3.104%	$45.1183	$45.12	$45.10	$45.10
Purchase #2	$128.51	8.593%	$139.5529	$139.55	$139.55	$139.60
Purchase #3	$212.49	7.585%	$228.6074	$228.61	$228.60	$228.60
Purchase #4	$117.30	7.454%	$126.0435	$126.04	$126.05	$126.00
Purchase #5	$46.65	4.720%	$48.8519	$48.85	$48.85	$48.90
Purchase #6	$243.83	5.601%	$257.4869	$257.49	$257.50	$257.50
Purchase #7	$46.83	12.290%	$52.5854	$52.59	$52.60	$52.60
7 purchase totals =	$839.37		$898.2463	$898.25	$898.25	$898.30