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	$104.42	6.445%	$111.1499	$111.15	$111.15	$111.10
Purchase #2	$44.38	8.817%	$48.293	$48.29	$48.30	$48.30
Purchase #3	$85.43	12.279%	$95.9199	$95.92	$95.90	$95.90
Purchase #4	$26.41	12.856%	$29.8053	$29.81	$29.80	$29.80
Purchase #5	$183.94	7.829%	$198.3407	$198.34	$198.35	$198.30
Purchase #6	$127.50	12.225%	$143.0869	$143.09	$143.10	$143.10
Purchase #7	$30.40	11.828%	$33.9957	$34.00	$34.00	$34.00
7 purchase totals =	$602.48		$660.5914	$660.60	$660.60	$660.50