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	$24.43	11.138%	$27.151	$27.15	$27.15	$27.20
Purchase #2	$204.41	12.449%	$229.857	$229.86	$229.85	$229.90
Purchase #3	$184.62	3.387%	$190.8731	$190.87	$190.85	$190.90
Purchase #4	$91.45	10.246%	$100.82	$100.82	$100.80	$100.80
Purchase #5	$119.82	3.845%	$124.4271	$124.43	$124.45	$124.40
Purchase #6	$148.69	5.243%	$156.4858	$156.49	$156.50	$156.50
Purchase #7	$121.50	7.553%	$130.6769	$130.68	$130.70	$130.70
7 purchase totals =	$894.92		$960.2909	$960.30	$960.30	$960.40