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	$59.78	6.515%	$63.6747	$63.67	$63.65	$63.70
Purchase #2	$149.32	11.476%	$166.456	$166.46	$166.45	$166.50
Purchase #3	$41.64	4.534%	$43.528	$43.53	$43.55	$43.50
Purchase #4	$204.26	12.480%	$229.7516	$229.75	$229.75	$229.80
Purchase #5	$47.80	12.732%	$53.8859	$53.89	$53.90	$53.90
Purchase #6	$12.56	10.126%	$13.8318	$13.83	$13.85	$13.80
Purchase #7	$204.37	12.756%	$230.4394	$230.44	$230.45	$230.40
7 purchase totals =	$719.73		$801.5674	$801.57	$801.60	$801.60