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	$6.35	3.832%	$6.5933	$6.59	$6.60	$6.60
Purchase #2	$112.64	13.119%	$127.4172	$127.42	$127.40	$127.40
Purchase #3	$117.34	10.394%	$129.5363	$129.54	$129.55	$129.50
Purchase #4	$234.65	8.855%	$255.4283	$255.43	$255.45	$255.40
Purchase #5	$145.49	9.763%	$159.6942	$159.69	$159.70	$159.70
Purchase #6	$184.30	4.726%	$193.01	$193.01	$193.00	$193.00
Purchase #7	$205.72	8.694%	$223.6053	$223.61	$223.60	$223.60
7 purchase totals =	$1,006.49		$1,095.2846	$1,095.29	$1,095.30	$1,095.20