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	$170.61	8.685%	$185.4275	$185.43	$185.45	$185.40
Purchase #2	$44.39	9.321%	$48.5276	$48.53	$48.55	$48.50
Purchase #3	$210.83	10.770%	$233.5364	$233.54	$233.55	$233.50
Purchase #4	$52.80	5.768%	$55.8455	$55.85	$55.85	$55.80
Purchase #5	$32.30	7.238%	$34.6379	$34.64	$34.65	$34.60
Purchase #6	$56.28	8.108%	$60.8432	$60.84	$60.85	$60.80
Purchase #7	$149.49	10.139%	$164.6468	$164.65	$164.65	$164.60
7 purchase totals =	$716.70		$783.4649	$783.48	$783.55	$783.20