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	$170.71	5.152%	$179.505	$179.51	$179.50	$179.50
Purchase #2	$96.69	4.323%	$100.8699	$100.87	$100.85	$100.90
Purchase #3	$179.85	3.317%	$185.8156	$185.82	$185.80	$185.80
Purchase #4	$51.88	9.722%	$56.9238	$56.92	$56.90	$56.90
Purchase #5	$8.71	6.176%	$9.2479	$9.25	$9.25	$9.20
Purchase #6	$205.93	7.246%	$220.8517	$220.85	$220.85	$220.90
Purchase #7	$50.32	8.516%	$54.6053	$54.61	$54.60	$54.60
7 purchase totals =	$764.09		$807.8192	$807.83	$807.75	$807.80