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	$84.29	9.660%	$92.4324	$92.43	$92.45	$92.40
Purchase #2	$216.98	8.781%	$236.033	$236.03	$236.05	$236.00
Purchase #3	$74.41	5.194%	$78.2749	$78.27	$78.25	$78.30
Purchase #4	$50.85	12.231%	$57.0695	$57.07	$57.05	$57.10
Purchase #5	$94.60	5.103%	$99.4274	$99.43	$99.45	$99.40
Purchase #6	$64.30	7.169%	$68.9097	$68.91	$68.90	$68.90
Purchase #7	$77.39	8.213%	$83.746	$83.75	$83.75	$83.70
7 purchase totals =	$662.82		$715.8929	$715.89	$715.90	$715.80