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	$11.48	5.764%	$12.1417	$12.14	$12.15	$12.10
Purchase #2	$132.27	5.407%	$139.4218	$139.42	$139.40	$139.40
Purchase #3	$40.65	3.145%	$41.9284	$41.93	$41.95	$41.90
Purchase #4	$85.65	5.588%	$90.4361	$90.44	$90.45	$90.40
Purchase #5	$51.85	13.378%	$58.7865	$58.79	$58.80	$58.80
Purchase #6	$104.47	6.845%	$111.621	$111.62	$111.60	$111.60
Purchase #7	$95.44	3.257%	$98.5485	$98.55	$98.55	$98.50
7 purchase totals =	$521.81		$552.8840	$552.89	$552.90	$552.70