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	$128.74	12.476%	$144.8016	$144.80	$144.80	$144.80
Purchase #2	$112.86	7.141%	$120.9193	$120.92	$120.90	$120.90
Purchase #3	$106.95	6.863%	$114.29	$114.29	$114.30	$114.30
Purchase #4	$99.41	4.615%	$103.9978	$104.00	$104.00	$104.00
Purchase #5	$96.85	3.150%	$99.9008	$99.90	$99.90	$99.90
Purchase #6	$18.39	10.189%	$20.2638	$20.26	$20.25	$20.30
Purchase #7	$158.37	13.228%	$179.3192	$179.32	$179.30	$179.30
7 purchase totals =	$721.57		$783.4925	$783.49	$783.45	$783.50