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	$221.68	8.528%	$240.5849	$240.58	$240.60	$240.60
Purchase #2	$248.25	4.277%	$258.8677	$258.87	$258.85	$258.90
Purchase #3	$37.88	5.106%	$39.8142	$39.81	$39.80	$39.80
Purchase #4	$167.90	13.388%	$190.3785	$190.38	$190.40	$190.40
Purchase #5	$168.91	9.622%	$185.1625	$185.16	$185.15	$185.20
Purchase #6	$187.66	9.258%	$205.0336	$205.03	$205.05	$205.00
Purchase #7	$160.70	4.718%	$168.2818	$168.28	$168.30	$168.30
7 purchase totals =	$1,192.98		$1,288.1232	$1,288.11	$1,288.15	$1,288.20