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	$34.43	9.301%	$37.6323	$37.63	$37.65	$37.60
Purchase #2	$218.46	11.653%	$243.9171	$243.92	$243.90	$243.90
Purchase #3	$38.92	11.677%	$43.4647	$43.46	$43.45	$43.50
Purchase #4	$248.51	3.354%	$256.845	$256.85	$256.85	$256.80
Purchase #5	$62.85	8.625%	$68.2708	$68.27	$68.25	$68.30
Purchase #6	$10.66	13.516%	$12.1008	$12.10	$12.10	$12.10
Purchase #7	$232.79	9.286%	$254.4069	$254.41	$254.40	$254.40
7 purchase totals =	$846.62		$916.6376	$916.64	$916.60	$916.60