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	$10.30	13.777%	$11.719	$11.72	$11.70	$11.70
Purchase #2	$37.32	13.857%	$42.4914	$42.49	$42.50	$42.50
Purchase #3	$133.61	13.400%	$151.5137	$151.51	$151.50	$151.50
Purchase #4	$39.83	12.722%	$44.8972	$44.90	$44.90	$44.90
Purchase #5	$26.37	5.845%	$27.9113	$27.91	$27.90	$27.90
Purchase #6	$66.28	12.235%	$74.3894	$74.39	$74.40	$74.40
Purchase #7	$214.43	12.314%	$240.8349	$240.83	$240.85	$240.80
7 purchase totals =	$528.14		$593.7569	$593.75	$593.75	$593.70