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	$20.63	12.574%	$23.224	$23.22	$23.20	$23.20
Purchase #2	$120.39	10.151%	$132.6108	$132.61	$132.60	$132.60
Purchase #3	$101.39	8.797%	$110.3093	$110.31	$110.30	$110.30
Purchase #4	$101.42	10.146%	$111.7101	$111.71	$111.70	$111.70
Purchase #5	$118.47	7.244%	$127.052	$127.05	$127.05	$127.10
Purchase #6	$55.98	8.248%	$60.5972	$60.60	$60.60	$60.60
Purchase #7	$7.65	10.170%	$8.428	$8.43	$8.45	$8.40
7 purchase totals =	$525.93		$573.9314	$573.93	$573.90	$573.90