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	$39.44	7.846%	$42.5345	$42.53	$42.55	$42.50
Purchase #2	$59.71	4.214%	$62.2262	$62.23	$62.25	$62.20
Purchase #3	$9.72	13.194%	$11.0025	$11.00	$11.00	$11.00
Purchase #4	$53.94	5.111%	$56.6969	$56.70	$56.70	$56.70
Purchase #5	$189.87	9.772%	$208.4241	$208.42	$208.40	$208.40
Purchase #6	$65.79	10.347%	$72.5973	$72.60	$72.60	$72.60
Purchase #7	$71.93	11.307%	$80.0631	$80.06	$80.05	$80.10
7 purchase totals =	$490.40		$533.5446	$533.54	$533.55	$533.50