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	$16.41	12.532%	$18.4665	$18.47	$18.45	$18.50
Purchase #2	$53.83	9.671%	$59.0359	$59.04	$59.05	$59.00
Purchase #3	$151.90	4.611%	$158.9041	$158.90	$158.90	$158.90
Purchase #4	$195.28	11.317%	$217.3798	$217.38	$217.40	$217.40
Purchase #5	$57.93	7.671%	$62.3738	$62.37	$62.35	$62.40
Purchase #6	$240.76	5.859%	$254.8661	$254.87	$254.85	$254.90
Purchase #7	$28.83	7.204%	$30.9069	$30.91	$30.90	$30.90
7 purchase totals =	$744.94		$801.9331	$801.94	$801.90	$802.00