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	$11.29	6.547%	$12.0292	$12.03	$12.05	$12.00
Purchase #2	$45.33	9.128%	$49.4677	$49.47	$49.45	$49.50
Purchase #3	$96.45	5.556%	$101.8088	$101.81	$101.80	$101.80
Purchase #4	$12.48	11.345%	$13.8959	$13.90	$13.90	$13.90
Purchase #5	$16.43	13.298%	$18.6149	$18.61	$18.60	$18.60
Purchase #6	$224.54	13.774%	$255.4681	$255.47	$255.45	$255.50
Purchase #7	$138.60	4.658%	$145.056	$145.06	$145.05	$145.10
7 purchase totals =	$545.12		$596.3406	$596.35	$596.30	$596.40