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	$48.59	11.137%	$54.0015	$54.00	$54.00	$54.00
Purchase #2	$50.89	8.335%	$55.1317	$55.13	$55.15	$55.10
Purchase #3	$83.44	7.784%	$89.935	$89.94	$89.95	$89.90
Purchase #4	$95.79	3.867%	$99.4942	$99.49	$99.50	$99.50
Purchase #5	$38.75	10.515%	$42.8246	$42.82	$42.80	$42.80
Purchase #6	$196.56	4.717%	$205.8317	$205.83	$205.85	$205.80
Purchase #7	$127.62	4.828%	$133.7815	$133.78	$133.80	$133.80
7 purchase totals =	$641.64		$681.0002	$680.99	$681.05	$680.90