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	$150.64	6.114%	$159.8501	$159.85	$159.85	$159.90
Purchase #2	$63.99	12.146%	$71.7622	$71.76	$71.75	$71.80
Purchase #3	$87.26	13.588%	$99.1169	$99.12	$99.10	$99.10
Purchase #4	$40.31	5.465%	$42.5129	$42.51	$42.50	$42.50
Purchase #5	$245.29	8.845%	$266.9859	$266.99	$267.00	$267.00
Purchase #6	$139.92	13.119%	$158.2761	$158.28	$158.30	$158.30
Purchase #7	$32.73	4.258%	$34.1236	$34.12	$34.10	$34.10
7 purchase totals =	$760.14		$832.6277	$832.63	$832.60	$832.70