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	$96.68	8.785%	$105.1733	$105.17	$105.15	$105.20
Purchase #2	$98.93	13.115%	$111.9047	$111.90	$111.90	$111.90
Purchase #3	$138.76	6.720%	$148.0847	$148.08	$148.10	$148.10
Purchase #4	$94.74	11.220%	$105.3698	$105.37	$105.35	$105.40
Purchase #5	$110.64	12.357%	$124.3118	$124.31	$124.30	$124.30
Purchase #6	$55.60	5.478%	$58.6458	$58.65	$58.65	$58.60
Purchase #7	$209.78	5.548%	$221.4186	$221.42	$221.40	$221.40
7 purchase totals =	$805.13		$874.9087	$874.90	$874.85	$874.90