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	$124.70	10.867%	$138.2511	$138.25	$138.25	$138.30
Purchase #2	$42.91	5.176%	$45.131	$45.13	$45.15	$45.10
Purchase #3	$59.85	5.722%	$63.2746	$63.27	$63.25	$63.30
Purchase #4	$80.47	12.789%	$90.7613	$90.76	$90.75	$90.80
Purchase #5	$211.75	13.466%	$240.2643	$240.26	$240.25	$240.30
Purchase #6	$222.29	8.574%	$241.3491	$241.35	$241.35	$241.30
Purchase #7	$12.93	10.783%	$14.3242	$14.32	$14.30	$14.30
7 purchase totals =	$754.90		$833.3556	$833.34	$833.30	$833.40