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	$132.71	12.148%	$148.8316	$148.83	$148.85	$148.80
Purchase #2	$144.44	3.271%	$149.1646	$149.16	$149.15	$149.20
Purchase #3	$214.30	6.631%	$228.5102	$228.51	$228.50	$228.50
Purchase #4	$97.78	6.177%	$103.8199	$103.82	$103.80	$103.80
Purchase #5	$34.29	10.659%	$37.945	$37.95	$37.95	$37.90
Purchase #6	$100.26	12.352%	$112.6441	$112.64	$112.65	$112.60
Purchase #7	$191.64	4.193%	$199.6755	$199.68	$199.70	$199.70
7 purchase totals =	$915.42		$980.5909	$980.59	$980.60	$980.50