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	$11.67	7.337%	$12.5262	$12.53	$12.55	$12.50
Purchase #2	$100.95	4.393%	$105.3847	$105.38	$105.40	$105.40
Purchase #3	$30.76	8.271%	$33.3042	$33.30	$33.30	$33.30
Purchase #4	$204.83	9.514%	$224.3175	$224.32	$224.30	$224.30
Purchase #5	$199.94	4.395%	$208.7274	$208.73	$208.75	$208.70
Purchase #6	$146.59	7.871%	$158.1281	$158.13	$158.15	$158.10
Purchase #7	$205.90	5.663%	$217.5601	$217.56	$217.55	$217.60
7 purchase totals =	$900.64		$959.9482	$959.95	$960.00	$959.90