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	$31.60	5.423%	$33.3137	$33.31	$33.30	$33.30
Purchase #2	$60.69	11.198%	$67.4861	$67.49	$67.50	$67.50
Purchase #3	$222.26	13.341%	$251.9117	$251.91	$251.90	$251.90
Purchase #4	$83.33	12.139%	$93.4454	$93.45	$93.45	$93.40
Purchase #5	$175.30	9.176%	$191.3855	$191.39	$191.40	$191.40
Purchase #6	$12.84	7.180%	$13.7619	$13.76	$13.75	$13.80
Purchase #7	$12.45	8.648%	$13.5267	$13.53	$13.55	$13.50
7 purchase totals =	$598.47		$664.8310	$664.84	$664.85	$664.80