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	$59.30	12.164%	$66.5133	$66.51	$66.50	$66.50
Purchase #2	$104.27	4.194%	$108.6431	$108.64	$108.65	$108.60
Purchase #3	$139.51	3.631%	$144.5756	$144.58	$144.60	$144.60
Purchase #4	$79.86	7.447%	$85.8072	$85.81	$85.80	$85.80
Purchase #5	$188.72	13.775%	$214.7162	$214.72	$214.70	$214.70
Purchase #6	$151.63	11.303%	$168.7687	$168.77	$168.75	$168.80
Purchase #7	$25.40	9.238%	$27.7465	$27.75	$27.75	$27.70
7 purchase totals =	$748.69		$816.7706	$816.78	$816.75	$816.70