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	$105.99	5.177%	$111.4771	$111.48	$111.50	$111.50
Purchase #2	$53.74	10.145%	$59.1919	$59.19	$59.20	$59.20
Purchase #3	$219.39	13.822%	$249.7141	$249.71	$249.70	$249.70
Purchase #4	$14.28	10.701%	$15.8081	$15.81	$15.80	$15.80
Purchase #5	$131.91	13.872%	$150.2086	$150.21	$150.20	$150.20
Purchase #6	$59.74	13.237%	$67.6478	$67.65	$67.65	$67.60
Purchase #7	$145.82	4.191%	$151.9313	$151.93	$151.95	$151.90
7 purchase totals =	$730.87		$805.9789	$805.98	$806.00	$805.90