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	$49.27	6.783%	$52.612	$52.61	$52.60	$52.60
Purchase #2	$129.97	9.584%	$142.4263	$142.43	$142.45	$142.40
Purchase #3	$53.52	13.715%	$60.8603	$60.86	$60.85	$60.90
Purchase #4	$45.86	9.661%	$50.2905	$50.29	$50.30	$50.30
Purchase #5	$171.77	10.771%	$190.2713	$190.27	$190.25	$190.30
Purchase #6	$101.98	12.332%	$114.5562	$114.56	$114.55	$114.60
Purchase #7	$15.77	6.292%	$16.7622	$16.76	$16.75	$16.80
7 purchase totals =	$568.14		$627.7788	$627.78	$627.75	$627.90