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	$121.87	5.467%	$128.5326	$128.53	$128.55	$128.50
Purchase #2	$141.60	4.581%	$148.0867	$148.09	$148.10	$148.10
Purchase #3	$111.70	7.182%	$119.7223	$119.72	$119.70	$119.70
Purchase #4	$39.62	8.624%	$43.0368	$43.04	$43.05	$43.00
Purchase #5	$52.69	3.467%	$54.5168	$54.52	$54.50	$54.50
Purchase #6	$39.87	13.701%	$45.3326	$45.33	$45.35	$45.30
Purchase #7	$140.51	13.205%	$159.0643	$159.06	$159.05	$159.10
7 purchase totals =	$647.86		$698.2921	$698.29	$698.30	$698.20