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	$28.54	10.803%	$31.6232	$31.62	$31.60	$31.60
Purchase #2	$73.33	6.485%	$78.0855	$78.09	$78.10	$78.10
Purchase #3	$32.52	3.446%	$33.6406	$33.64	$33.65	$33.60
Purchase #4	$141.60	9.135%	$154.5352	$154.54	$154.55	$154.50
Purchase #5	$145.45	5.522%	$153.4817	$153.48	$153.50	$153.50
Purchase #6	$45.76	4.211%	$47.687	$47.69	$47.70	$47.70
Purchase #7	$101.55	9.721%	$111.4217	$111.42	$111.40	$111.40
7 purchase totals =	$568.75		$610.4749	$610.48	$610.50	$610.40