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	$220.57	9.758%	$242.0932	$242.09	$242.10	$242.10
Purchase #2	$41.90	10.172%	$46.1621	$46.16	$46.15	$46.20
Purchase #3	$178.97	9.611%	$196.1708	$196.17	$196.15	$196.20
Purchase #4	$60.38	4.445%	$63.0639	$63.06	$63.05	$63.10
Purchase #5	$52.94	3.124%	$54.5938	$54.59	$54.60	$54.60
Purchase #6	$73.59	7.731%	$79.2792	$79.28	$79.30	$79.30
Purchase #7	$90.68	9.517%	$99.31	$99.31	$99.30	$99.30
7 purchase totals =	$719.03		$780.6730	$780.66	$780.65	$780.80