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	$89.61	11.485%	$99.9017	$99.90	$99.90	$99.90
Purchase #2	$112.59	12.532%	$126.6998	$126.70	$126.70	$126.70
Purchase #3	$111.40	6.276%	$118.3915	$118.39	$118.40	$118.40
Purchase #4	$239.32	10.428%	$264.2763	$264.28	$264.30	$264.30
Purchase #5	$231.87	3.762%	$240.5929	$240.59	$240.60	$240.60
Purchase #6	$9.58	13.726%	$10.895	$10.90	$10.90	$10.90
Purchase #7	$65.49	5.127%	$68.8477	$68.85	$68.85	$68.80
7 purchase totals =	$859.86		$929.6049	$929.61	$929.65	$929.60