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	$15.49	10.848%	$17.1704	$17.17	$17.15	$17.20
Purchase #2	$91.46	4.222%	$95.3214	$95.32	$95.30	$95.30
Purchase #3	$57.92	4.649%	$60.6127	$60.61	$60.60	$60.60
Purchase #4	$91.38	8.638%	$99.2734	$99.27	$99.25	$99.30
Purchase #5	$34.83	11.201%	$38.7313	$38.73	$38.75	$38.70
Purchase #6	$100.55	4.462%	$105.0365	$105.04	$105.05	$105.00
Purchase #7	$102.70	12.432%	$115.4677	$115.47	$115.45	$115.50
7 purchase totals =	$494.33		$531.6134	$531.61	$531.55	$531.60