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	$66.54	5.688%	$70.3248	$70.32	$70.30	$70.30
Purchase #2	$106.71	7.562%	$114.7794	$114.78	$114.80	$114.80
Purchase #3	$70.54	3.308%	$72.8735	$72.87	$72.85	$72.90
Purchase #4	$45.52	12.648%	$51.2774	$51.28	$51.30	$51.30
Purchase #5	$153.75	4.607%	$160.8333	$160.83	$160.85	$160.80
Purchase #6	$205.88	10.751%	$228.0142	$228.01	$228.00	$228.00
Purchase #7	$36.64	10.286%	$40.4088	$40.41	$40.40	$40.40
7 purchase totals =	$685.58		$738.5114	$738.50	$738.50	$738.50