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	$180.51	5.374%	$190.2106	$190.21	$190.20	$190.20
Purchase #2	$98.86	9.837%	$108.5849	$108.58	$108.60	$108.60
Purchase #3	$100.72	11.108%	$111.908	$111.91	$111.90	$111.90
Purchase #4	$72.47	8.623%	$78.7191	$78.72	$78.70	$78.70
Purchase #5	$93.80	6.671%	$100.0574	$100.06	$100.05	$100.10
Purchase #6	$202.72	8.485%	$219.9208	$219.92	$219.90	$219.90
Purchase #7	$37.55	6.762%	$40.0891	$40.09	$40.10	$40.10
7 purchase totals =	$786.63		$849.4899	$849.49	$849.45	$849.50