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	$20.27	10.323%	$22.3625	$22.36	$22.35	$22.40
Purchase #2	$248.38	12.113%	$278.4663	$278.47	$278.45	$278.50
Purchase #3	$190.30	11.738%	$212.6374	$212.64	$212.65	$212.60
Purchase #4	$203.85	7.830%	$219.8115	$219.81	$219.80	$219.80
Purchase #5	$62.60	4.127%	$65.1835	$65.18	$65.20	$65.20
Purchase #6	$91.82	8.754%	$99.8579	$99.86	$99.85	$99.90
Purchase #7	$27.61	7.729%	$29.744	$29.74	$29.75	$29.70
7 purchase totals =	$844.83		$928.0631	$928.06	$928.05	$928.10