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	$198.44	11.492%	$221.2447	$221.24	$221.25	$221.20
Purchase #2	$62.90	4.580%	$65.7808	$65.78	$65.80	$65.80
Purchase #3	$82.80	11.407%	$92.245	$92.25	$92.25	$92.20
Purchase #4	$129.52	3.165%	$133.6193	$133.62	$133.60	$133.60
Purchase #5	$95.85	11.713%	$107.0769	$107.08	$107.10	$107.10
Purchase #6	$102.93	8.363%	$111.538	$111.54	$111.55	$111.50
Purchase #7	$215.54	10.548%	$238.2752	$238.28	$238.30	$238.30
7 purchase totals =	$887.98		$969.7799	$969.79	$969.85	$969.70