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	$27.65	5.188%	$29.0845	$29.08	$29.10	$29.10
Purchase #2	$82.98	10.325%	$91.5477	$91.55	$91.55	$91.50
Purchase #3	$66.41	8.411%	$71.9957	$72.00	$72.00	$72.00
Purchase #4	$57.49	8.487%	$62.3692	$62.37	$62.35	$62.40
Purchase #5	$90.92	8.317%	$98.4818	$98.48	$98.50	$98.50
Purchase #6	$45.87	11.130%	$50.9753	$50.98	$51.00	$51.00
Purchase #7	$132.37	9.650%	$145.1437	$145.14	$145.15	$145.10
7 purchase totals =	$503.69		$549.5979	$549.60	$549.65	$549.60