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	$203.83	13.136%	$230.6051	$230.61	$230.60	$230.60
Purchase #2	$200.76	13.455%	$227.7723	$227.77	$227.75	$227.80
Purchase #3	$159.53	9.463%	$174.6263	$174.63	$174.65	$174.60
Purchase #4	$149.53	4.766%	$156.6566	$156.66	$156.65	$156.70
Purchase #5	$80.63	11.177%	$89.642	$89.64	$89.65	$89.60
Purchase #6	$32.28	5.102%	$33.9269	$33.93	$33.95	$33.90
Purchase #7	$111.69	4.789%	$117.0388	$117.04	$117.05	$117.00
7 purchase totals =	$938.25		$1,030.2680	$1,030.28	$1,030.30	$1,030.20