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	$249.66	11.310%	$277.8965	$277.90	$277.90	$277.90
Purchase #2	$126.57	8.725%	$137.6132	$137.61	$137.60	$137.60
Purchase #3	$167.90	7.810%	$181.013	$181.01	$181.00	$181.00
Purchase #4	$234.89	13.311%	$266.1562	$266.16	$266.15	$266.20
Purchase #5	$242.70	8.714%	$263.8489	$263.85	$263.85	$263.80
Purchase #6	$44.65	3.671%	$46.2891	$46.29	$46.30	$46.30
Purchase #7	$173.61	13.286%	$196.6758	$196.68	$196.70	$196.70
7 purchase totals =	$1,239.98		$1,369.4927	$1,369.50	$1,369.50	$1,369.50