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	$77.49	6.451%	$82.4889	$82.49	$82.50	$82.50
Purchase #2	$43.37	12.677%	$48.868	$48.87	$48.85	$48.90
Purchase #3	$126.99	4.217%	$132.3452	$132.35	$132.35	$132.30
Purchase #4	$115.73	13.694%	$131.5781	$131.58	$131.60	$131.60
Purchase #5	$249.42	5.798%	$263.8814	$263.88	$263.90	$263.90
Purchase #6	$200.81	10.192%	$221.2766	$221.28	$221.30	$221.30
Purchase #7	$239.52	13.231%	$271.2109	$271.21	$271.20	$271.20
7 purchase totals =	$1,053.33		$1,151.6491	$1,151.66	$1,151.70	$1,151.70