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	$137.51	12.516%	$154.7208	$154.72	$154.70	$154.70
Purchase #2	$32.52	8.547%	$35.2995	$35.30	$35.30	$35.30
Purchase #3	$161.60	12.524%	$181.8388	$181.84	$181.85	$181.80
Purchase #4	$48.86	10.133%	$53.811	$53.81	$53.80	$53.80
Purchase #5	$91.37	9.296%	$99.8638	$99.86	$99.85	$99.90
Purchase #6	$118.51	5.139%	$124.6002	$124.60	$124.60	$124.60
Purchase #7	$223.78	4.587%	$234.0448	$234.04	$234.05	$234.00
7 purchase totals =	$814.15		$884.1789	$884.17	$884.15	$884.10