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	$16.94	10.463%	$18.7124	$18.71	$18.70	$18.70
Purchase #2	$142.70	4.324%	$148.8703	$148.87	$148.85	$148.90
Purchase #3	$39.65	13.852%	$45.1423	$45.14	$45.15	$45.10
Purchase #4	$69.34	12.284%	$77.8577	$77.86	$77.85	$77.90
Purchase #5	$123.89	3.429%	$128.1382	$128.14	$128.15	$128.10
Purchase #6	$233.80	5.673%	$247.0635	$247.06	$247.05	$247.10
Purchase #7	$72.61	12.473%	$81.6666	$81.67	$81.65	$81.70
7 purchase totals =	$698.93		$747.4510	$747.45	$747.40	$747.50