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	$19.56	9.768%	$21.4706	$21.47	$21.45	$21.50
Purchase #2	$115.32	11.396%	$128.4619	$128.46	$128.45	$128.50
Purchase #3	$126.77	4.219%	$132.1184	$132.12	$132.10	$132.10
Purchase #4	$124.89	5.385%	$131.6153	$131.62	$131.60	$131.60
Purchase #5	$211.57	10.391%	$233.5542	$233.55	$233.55	$233.60
Purchase #6	$98.81	4.839%	$103.5914	$103.59	$103.60	$103.60
Purchase #7	$13.46	12.559%	$15.1504	$15.15	$15.15	$15.20
7 purchase totals =	$710.38		$765.9622	$765.96	$765.90	$766.10