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	$249.98	6.613%	$266.5112	$266.51	$266.50	$266.50
Purchase #2	$134.94	13.833%	$153.6063	$153.61	$153.60	$153.60
Purchase #3	$163.36	13.403%	$185.2551	$185.26	$185.25	$185.30
Purchase #4	$95.59	4.422%	$99.817	$99.82	$99.80	$99.80
Purchase #5	$118.66	13.631%	$134.8345	$134.83	$134.85	$134.80
Purchase #6	$178.75	6.679%	$190.6887	$190.69	$190.70	$190.70
Purchase #7	$182.38	5.228%	$191.9148	$191.91	$191.90	$191.90
7 purchase totals =	$1,123.66		$1,222.6276	$1,222.63	$1,222.60	$1,222.60