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	$48.51	4.315%	$50.6032	$50.60	$50.60	$50.60
Purchase #2	$46.98	13.822%	$53.4736	$53.47	$53.45	$53.50
Purchase #3	$139.35	6.836%	$148.876	$148.88	$148.90	$148.90
Purchase #4	$75.59	5.297%	$79.594	$79.59	$79.60	$79.60
Purchase #5	$125.70	13.689%	$142.9071	$142.91	$142.90	$142.90
Purchase #6	$148.51	4.170%	$154.7029	$154.70	$154.70	$154.70
Purchase #7	$32.32	5.208%	$34.0032	$34.00	$34.00	$34.00
7 purchase totals =	$616.96		$664.1600	$664.15	$664.15	$664.20