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	$43.85	12.799%	$49.4624	$49.46	$49.45	$49.50
Purchase #2	$72.98	5.578%	$77.0508	$77.05	$77.05	$77.10
Purchase #3	$89.51	12.616%	$100.8026	$100.80	$100.80	$100.80
Purchase #4	$9.75	3.726%	$10.1133	$10.11	$10.10	$10.10
Purchase #5	$66.78	9.233%	$72.9458	$72.95	$72.95	$72.90
Purchase #6	$191.32	10.603%	$211.6057	$211.61	$211.60	$211.60
Purchase #7	$133.62	5.176%	$140.5362	$140.54	$140.55	$140.50
7 purchase totals =	$607.81		$662.5168	$662.52	$662.50	$662.50