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	$140.90	12.559%	$158.5956	$158.60	$158.60	$158.60
Purchase #2	$145.61	8.695%	$158.2708	$158.27	$158.25	$158.30
Purchase #3	$177.50	6.260%	$188.6115	$188.61	$188.60	$188.60
Purchase #4	$215.65	12.699%	$243.0354	$243.04	$243.05	$243.00
Purchase #5	$42.82	13.263%	$48.4992	$48.50	$48.50	$48.50
Purchase #6	$75.61	3.722%	$78.4242	$78.42	$78.40	$78.40
Purchase #7	$92.60	13.572%	$105.1677	$105.17	$105.15	$105.20
7 purchase totals =	$890.69		$980.6044	$980.61	$980.55	$980.60