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	$91.48	10.296%	$100.8988	$100.90	$100.90	$100.90
Purchase #2	$225.81	12.707%	$254.5037	$254.50	$254.50	$254.50
Purchase #3	$174.31	12.758%	$196.5485	$196.55	$196.55	$196.50
Purchase #4	$11.45	5.584%	$12.0894	$12.09	$12.10	$12.10
Purchase #5	$207.87	4.704%	$217.6482	$217.65	$217.65	$217.60
Purchase #6	$130.76	11.605%	$145.9347	$145.93	$145.95	$145.90
Purchase #7	$45.79	8.487%	$49.6762	$49.68	$49.70	$49.70
7 purchase totals =	$887.47		$977.2995	$977.30	$977.35	$977.20