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	$49.69	5.293%	$52.3201	$52.32	$52.30	$52.30
Purchase #2	$36.62	12.292%	$41.1213	$41.12	$41.10	$41.10
Purchase #3	$160.95	3.458%	$166.5157	$166.52	$166.50	$166.50
Purchase #4	$56.74	4.126%	$59.0811	$59.08	$59.10	$59.10
Purchase #5	$118.47	7.300%	$127.1183	$127.12	$127.10	$127.10
Purchase #6	$9.65	6.267%	$10.2548	$10.25	$10.25	$10.30
Purchase #7	$123.67	5.185%	$130.0823	$130.08	$130.10	$130.10
7 purchase totals =	$555.79		$586.4936	$586.49	$586.45	$586.50