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	$15.95	12.763%	$17.9857	$17.99	$18.00	$18.00
Purchase #2	$186.47	6.866%	$199.273	$199.27	$199.25	$199.30
Purchase #3	$180.80	3.731%	$187.5456	$187.55	$187.55	$187.50
Purchase #4	$105.49	5.690%	$111.4924	$111.49	$111.50	$111.50
Purchase #5	$145.59	10.554%	$160.9556	$160.96	$160.95	$161.00
Purchase #6	$118.98	6.747%	$127.0076	$127.01	$127.00	$127.00
Purchase #7	$248.76	11.859%	$278.2604	$278.26	$278.25	$278.30
7 purchase totals =	$1,002.04		$1,082.5203	$1,082.53	$1,082.50	$1,082.60