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	3.689%	$128.2633	$128.26	$128.25	$128.30
Purchase #2	$100.98	9.436%	$110.5085	$110.51	$110.50	$110.50
Purchase #3	$173.98	12.674%	$196.0302	$196.03	$196.05	$196.00
Purchase #4	$114.45	6.324%	$121.6878	$121.69	$121.70	$121.70
Purchase #5	$37.97	11.592%	$42.3715	$42.37	$42.35	$42.40
Purchase #6	$115.31	10.716%	$127.6666	$127.67	$127.65	$127.70
Purchase #7	$71.89	4.141%	$74.867	$74.87	$74.85	$74.90
7 purchase totals =	$738.28		$801.3949	$801.40	$801.35	$801.50