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	$94.85	13.263%	$107.43	$107.43	$107.45	$107.40
Purchase #2	$87.50	3.824%	$90.846	$90.85	$90.85	$90.80
Purchase #3	$49.49	13.703%	$56.2716	$56.27	$56.25	$56.30
Purchase #4	$48.52	4.440%	$50.6743	$50.67	$50.65	$50.70
Purchase #5	$172.25	5.447%	$181.6325	$181.63	$181.65	$181.60
Purchase #6	$20.74	10.635%	$22.9457	$22.95	$22.95	$22.90
Purchase #7	$9.86	6.554%	$10.5062	$10.51	$10.50	$10.50
7 purchase totals =	$483.21		$520.3063	$520.31	$520.30	$520.20