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	$100.50	10.714%	$111.2676	$111.27	$111.25	$111.30
Purchase #2	$87.55	11.285%	$97.43	$97.43	$97.45	$97.40
Purchase #3	$35.94	10.136%	$39.5829	$39.58	$39.60	$39.60
Purchase #4	$226.38	8.282%	$245.1288	$245.13	$245.15	$245.10
Purchase #5	$30.90	11.716%	$34.5202	$34.52	$34.50	$34.50
Purchase #6	$86.52	10.815%	$95.8771	$95.88	$95.90	$95.90
Purchase #7	$49.32	11.173%	$54.8305	$54.83	$54.85	$54.80
7 purchase totals =	$617.11		$678.6371	$678.64	$678.70	$678.60