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	$6.90	8.543%	$7.4895	$7.49	$7.50	$7.50
Purchase #2	$104.95	6.142%	$111.396	$111.40	$111.40	$111.40
Purchase #3	$49.75	10.327%	$54.8877	$54.89	$54.90	$54.90
Purchase #4	$113.63	11.761%	$126.994	$126.99	$127.00	$127.00
Purchase #5	$28.67	12.344%	$32.209	$32.21	$32.20	$32.20
Purchase #6	$115.27	4.829%	$120.8364	$120.84	$120.85	$120.80
Purchase #7	$43.87	6.543%	$46.7404	$46.74	$46.75	$46.70
7 purchase totals =	$463.04		$500.5530	$500.56	$500.60	$500.50