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	$14.55	6.186%	$15.4501	$15.45	$15.45	$15.50
Purchase #2	$144.70	7.158%	$155.0576	$155.06	$155.05	$155.10
Purchase #3	$34.35	5.629%	$36.2836	$36.28	$36.30	$36.30
Purchase #4	$37.35	10.156%	$41.1433	$41.14	$41.15	$41.10
Purchase #5	$153.95	9.541%	$168.6384	$168.64	$168.65	$168.60
Purchase #6	$91.75	8.397%	$99.4542	$99.45	$99.45	$99.50
Purchase #7	$114.81	11.591%	$128.1176	$128.12	$128.10	$128.10
7 purchase totals =	$591.46		$644.1448	$644.14	$644.15	$644.20