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	$46.39	6.689%	$49.493	$49.49	$49.50	$49.50
Purchase #2	$19.86	11.680%	$22.1796	$22.18	$22.20	$22.20
Purchase #3	$170.51	12.788%	$192.3148	$192.31	$192.30	$192.30
Purchase #4	$108.68	9.104%	$118.5742	$118.57	$118.55	$118.60
Purchase #5	$125.72	11.182%	$139.778	$139.78	$139.80	$139.80
Purchase #6	$59.35	13.865%	$67.5789	$67.58	$67.60	$67.60
Purchase #7	$86.96	9.866%	$95.5395	$95.54	$95.55	$95.50
7 purchase totals =	$617.47		$685.4580	$685.45	$685.50	$685.50