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	$100.55	11.856%	$112.4712	$112.47	$112.45	$112.50
Purchase #2	$127.49	7.477%	$137.0224	$137.02	$137.00	$137.00
Purchase #3	$47.47	5.404%	$50.0353	$50.04	$50.05	$50.00
Purchase #4	$195.74	8.448%	$212.2761	$212.28	$212.30	$212.30
Purchase #5	$97.82	11.488%	$109.0576	$109.06	$109.05	$109.10
Purchase #6	$163.83	7.103%	$175.4668	$175.47	$175.45	$175.50
Purchase #7	$10.31	5.325%	$10.859	$10.86	$10.85	$10.90
7 purchase totals =	$743.21		$807.1884	$807.20	$807.15	$807.30