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	$100.72	8.307%	$109.0868	$109.09	$109.10	$109.10
Purchase #2	$107.73	4.624%	$112.7114	$112.71	$112.70	$112.70
Purchase #3	$54.27	6.520%	$57.8084	$57.81	$57.80	$57.80
Purchase #4	$211.52	10.369%	$233.4525	$233.45	$233.45	$233.50
Purchase #5	$34.71	13.150%	$39.2744	$39.27	$39.25	$39.30
Purchase #6	$151.37	5.749%	$160.0723	$160.07	$160.05	$160.10
Purchase #7	$61.59	12.464%	$69.2666	$69.27	$69.25	$69.30
7 purchase totals =	$721.91		$781.6724	$781.67	$781.60	$781.80