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	$171.29	10.864%	$189.8989	$189.90	$189.90	$189.90
Purchase #2	$155.48	11.664%	$173.6152	$173.62	$173.60	$173.60
Purchase #3	$175.37	3.696%	$181.8517	$181.85	$181.85	$181.90
Purchase #4	$177.99	5.364%	$187.5374	$187.54	$187.55	$187.50
Purchase #5	$214.32	6.253%	$227.7214	$227.72	$227.70	$227.70
Purchase #6	$54.43	12.350%	$61.1521	$61.15	$61.15	$61.20
Purchase #7	$247.81	4.492%	$258.9416	$258.94	$258.95	$258.90
7 purchase totals =	$1,196.69		$1,280.7183	$1,280.72	$1,280.70	$1,280.70