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	$27.50	11.522%	$30.6686	$30.67	$30.65	$30.70
Purchase #2	$200.35	7.199%	$214.7732	$214.77	$214.75	$214.80
Purchase #3	$59.82	11.192%	$66.5151	$66.52	$66.50	$66.50
Purchase #4	$89.67	12.194%	$100.6044	$100.60	$100.60	$100.60
Purchase #5	$27.27	11.343%	$30.3632	$30.36	$30.35	$30.40
Purchase #6	$30.57	10.683%	$33.8358	$33.84	$33.85	$33.80
Purchase #7	$78.36	7.845%	$84.5073	$84.51	$84.50	$84.50
7 purchase totals =	$513.54		$561.2676	$561.27	$561.20	$561.30