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	$40.38	5.841%	$42.7386	$42.74	$42.75	$42.70
Purchase #2	$247.72	3.334%	$255.979	$255.98	$256.00	$256.00
Purchase #3	$13.69	13.382%	$15.522	$15.52	$15.50	$15.50
Purchase #4	$17.68	10.866%	$19.6011	$19.60	$19.60	$19.60
Purchase #5	$79.59	4.158%	$82.8994	$82.90	$82.90	$82.90
Purchase #6	$123.63	6.286%	$131.4014	$131.40	$131.40	$131.40
Purchase #7	$108.57	11.789%	$121.3693	$121.37	$121.35	$121.40
7 purchase totals =	$631.26		$669.5108	$669.51	$669.50	$669.50