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	$153.32	9.177%	$167.3902	$167.39	$167.40	$167.40
Purchase #2	$128.70	7.800%	$138.7386	$138.74	$138.75	$138.70
Purchase #3	$89.62	10.527%	$99.0543	$99.05	$99.05	$99.10
Purchase #4	$132.85	9.113%	$144.9566	$144.96	$144.95	$145.00
Purchase #5	$68.58	12.326%	$77.0332	$77.03	$77.05	$77.00
Purchase #6	$114.30	12.676%	$128.7887	$128.79	$128.80	$128.80
Purchase #7	$75.78	10.127%	$83.4542	$83.45	$83.45	$83.50
7 purchase totals =	$763.15		$839.4158	$839.41	$839.45	$839.50