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	$123.70	13.311%	$140.1657	$140.17	$140.15	$140.20
Purchase #2	$220.96	5.616%	$233.3691	$233.37	$233.35	$233.40
Purchase #3	$151.75	4.409%	$158.4407	$158.44	$158.45	$158.40
Purchase #4	$55.93	6.142%	$59.3652	$59.37	$59.35	$59.40
Purchase #5	$10.87	13.713%	$12.3606	$12.36	$12.35	$12.40
Purchase #6	$208.47	5.634%	$220.2152	$220.22	$220.20	$220.20
Purchase #7	$100.81	11.660%	$112.5644	$112.56	$112.55	$112.60
7 purchase totals =	$872.49		$936.4809	$936.49	$936.40	$936.60