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	$85.74	6.742%	$91.5206	$91.52	$91.50	$91.50
Purchase #2	$156.51	9.116%	$170.7775	$170.78	$170.80	$170.80
Purchase #3	$62.58	13.176%	$70.8255	$70.83	$70.85	$70.80
Purchase #4	$51.57	11.831%	$57.6712	$57.67	$57.65	$57.70
Purchase #5	$217.50	7.145%	$233.0404	$233.04	$233.05	$233.00
Purchase #6	$237.77	12.269%	$266.942	$266.94	$266.95	$266.90
Purchase #7	$154.75	6.278%	$164.4652	$164.47	$164.45	$164.50
7 purchase totals =	$966.42		$1,055.2424	$1,055.25	$1,055.25	$1,055.20