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	$72.89	13.720%	$82.8905	$82.89	$82.90	$82.90
Purchase #2	$92.98	11.585%	$103.7517	$103.75	$103.75	$103.80
Purchase #3	$97.33	11.758%	$108.7741	$108.77	$108.75	$108.80
Purchase #4	$44.49	6.441%	$47.3556	$47.36	$47.35	$47.40
Purchase #5	$117.49	4.491%	$122.7665	$122.77	$122.75	$122.80
Purchase #6	$70.72	10.536%	$78.1711	$78.17	$78.15	$78.20
Purchase #7	$144.60	7.569%	$155.5448	$155.54	$155.55	$155.50
7 purchase totals =	$640.50		$699.2543	$699.25	$699.20	$699.40