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	$9.98	6.203%	$10.5991	$10.60	$10.60	$10.60
Purchase #2	$46.83	5.330%	$49.326	$49.33	$49.35	$49.30
Purchase #3	$126.40	11.371%	$140.7729	$140.77	$140.75	$140.80
Purchase #4	$53.45	11.595%	$59.6475	$59.65	$59.65	$59.60
Purchase #5	$156.64	8.501%	$169.956	$169.96	$169.95	$170.00
Purchase #6	$48.47	11.532%	$54.0596	$54.06	$54.05	$54.10
Purchase #7	$183.56	8.329%	$198.8487	$198.85	$198.85	$198.80
7 purchase totals =	$625.33		$683.2098	$683.22	$683.20	$683.20