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	$151.62	4.545%	$158.5111	$158.51	$158.50	$158.50
Purchase #2	$49.50	13.452%	$56.1587	$56.16	$56.15	$56.20
Purchase #3	$25.55	6.565%	$27.2274	$27.23	$27.25	$27.20
Purchase #4	$55.53	10.810%	$61.5328	$61.53	$61.55	$61.50
Purchase #5	$65.76	6.459%	$70.0074	$70.01	$70.00	$70.00
Purchase #6	$62.64	12.571%	$70.5145	$70.51	$70.50	$70.50
Purchase #7	$175.42	11.662%	$195.8775	$195.88	$195.90	$195.90
7 purchase totals =	$586.02		$639.8294	$639.83	$639.85	$639.80