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	$233.57	10.102%	$257.1652	$257.17	$257.15	$257.20
Purchase #2	$187.45	11.857%	$209.6759	$209.68	$209.70	$209.70
Purchase #3	$46.61	10.239%	$51.3824	$51.38	$51.40	$51.40
Purchase #4	$108.47	3.205%	$111.9465	$111.95	$111.95	$111.90
Purchase #5	$111.98	7.548%	$120.4323	$120.43	$120.45	$120.40
Purchase #6	$13.81	10.670%	$15.2835	$15.28	$15.30	$15.30
Purchase #7	$81.52	6.180%	$86.5579	$86.56	$86.55	$86.60
7 purchase totals =	$783.41		$852.4437	$852.45	$852.50	$852.50