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	$90.63	10.584%	$100.2223	$100.22	$100.20	$100.20
Purchase #2	$74.40	10.646%	$82.3206	$82.32	$82.30	$82.30
Purchase #3	$217.79	12.621%	$245.2773	$245.28	$245.30	$245.30
Purchase #4	$109.26	8.266%	$118.2914	$118.29	$118.30	$118.30
Purchase #5	$74.93	11.146%	$83.2817	$83.28	$83.30	$83.30
Purchase #6	$105.85	9.486%	$115.8909	$115.89	$115.90	$115.90
Purchase #7	$17.62	13.292%	$19.9621	$19.96	$19.95	$20.00
7 purchase totals =	$690.48		$765.2463	$765.24	$765.25	$765.30