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	$87.96	13.189%	$99.561	$99.56	$99.55	$99.60
Purchase #2	$178.49	6.523%	$190.1329	$190.13	$190.15	$190.10
Purchase #3	$132.98	13.634%	$151.1105	$151.11	$151.10	$151.10
Purchase #4	$200.53	11.741%	$224.0742	$224.07	$224.05	$224.10
Purchase #5	$214.52	8.625%	$233.0224	$233.02	$233.00	$233.00
Purchase #6	$49.62	12.476%	$55.8106	$55.81	$55.80	$55.80
Purchase #7	$19.80	5.667%	$20.9221	$20.92	$20.90	$20.90
7 purchase totals =	$883.90		$974.6337	$974.62	$974.55	$974.60