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	$238.86	7.572%	$256.9465	$256.95	$256.95	$256.90
Purchase #2	$205.96	5.120%	$216.5052	$216.51	$216.50	$216.50
Purchase #3	$40.51	5.495%	$42.736	$42.74	$42.75	$42.70
Purchase #4	$11.69	8.867%	$12.7266	$12.73	$12.75	$12.70
Purchase #5	$17.64	13.719%	$20.06	$20.06	$20.05	$20.10
Purchase #6	$37.35	9.321%	$40.8314	$40.83	$40.85	$40.80
Purchase #7	$19.73	10.700%	$21.8411	$21.84	$21.85	$21.80
7 purchase totals =	$571.74		$611.6468	$611.66	$611.70	$611.50