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	$195.39	13.610%	$221.9826	$221.98	$222.00	$222.00
Purchase #2	$149.76	3.243%	$154.6167	$154.62	$154.60	$154.60
Purchase #3	$175.55	10.297%	$193.6264	$193.63	$193.65	$193.60
Purchase #4	$198.50	5.196%	$208.8141	$208.81	$208.80	$208.80
Purchase #5	$42.84	12.127%	$48.0352	$48.04	$48.05	$48.00
Purchase #6	$77.64	7.243%	$83.2635	$83.26	$83.25	$83.30
Purchase #7	$182.72	4.228%	$190.4454	$190.45	$190.45	$190.40
7 purchase totals =	$1,022.40		$1,100.7839	$1,100.79	$1,100.80	$1,100.70