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	$150.88	5.319%	$158.9053	$158.91	$158.90	$158.90
Purchase #2	$5.71	7.868%	$6.1593	$6.16	$6.15	$6.20
Purchase #3	$239.79	13.379%	$271.8715	$271.87	$271.85	$271.90
Purchase #4	$194.71	11.277%	$216.6674	$216.67	$216.65	$216.70
Purchase #5	$140.30	10.637%	$155.2237	$155.22	$155.20	$155.20
Purchase #6	$105.87	5.392%	$111.5785	$111.58	$111.60	$111.60
Purchase #7	$55.72	6.235%	$59.1941	$59.19	$59.20	$59.20
7 purchase totals =	$892.98		$979.5998	$979.60	$979.55	$979.70