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	$194.55	13.705%	$221.2131	$221.21	$221.20	$221.20
Purchase #2	$44.37	12.471%	$49.9034	$49.90	$49.90	$49.90
Purchase #3	$127.51	13.799%	$145.1051	$145.11	$145.10	$145.10
Purchase #4	$155.83	5.773%	$164.8261	$164.83	$164.85	$164.80
Purchase #5	$45.70	5.182%	$48.0682	$48.07	$48.05	$48.10
Purchase #6	$118.86	3.718%	$123.2792	$123.28	$123.30	$123.30
Purchase #7	$125.48	6.135%	$133.1782	$133.18	$133.20	$133.20
7 purchase totals =	$812.30		$885.5733	$885.58	$885.60	$885.60