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	$109.44	10.388%	$120.8086	$120.81	$120.80	$120.80
Purchase #2	$17.83	11.366%	$19.8566	$19.86	$19.85	$19.90
Purchase #3	$238.77	6.152%	$253.4591	$253.46	$253.45	$253.50
Purchase #4	$50.45	6.617%	$53.7883	$53.79	$53.80	$53.80
Purchase #5	$76.41	3.868%	$79.3655	$79.37	$79.35	$79.40
Purchase #6	$109.32	13.378%	$123.9448	$123.94	$123.95	$123.90
Purchase #7	$120.62	13.693%	$137.1365	$137.14	$137.15	$137.10
7 purchase totals =	$722.84		$788.3594	$788.37	$788.35	$788.40