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	$111.47	4.745%	$116.7593	$116.76	$116.75	$116.80
Purchase #2	$233.79	12.720%	$263.5281	$263.53	$263.55	$263.50
Purchase #3	$16.66	10.585%	$18.4235	$18.42	$18.40	$18.40
Purchase #4	$232.46	5.447%	$245.1221	$245.12	$245.10	$245.10
Purchase #5	$82.46	10.260%	$90.9204	$90.92	$90.90	$90.90
Purchase #6	$91.47	10.114%	$100.7213	$100.72	$100.70	$100.70
Purchase #7	$127.48	12.345%	$143.2174	$143.22	$143.20	$143.20
7 purchase totals =	$895.79		$978.6921	$978.69	$978.60	$978.60