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	$111.92	10.142%	$123.2709	$123.27	$123.25	$123.30
Purchase #2	$198.31	3.720%	$205.6871	$205.69	$205.70	$205.70
Purchase #3	$60.31	3.838%	$62.6247	$62.62	$62.60	$62.60
Purchase #4	$94.60	11.475%	$105.4554	$105.46	$105.45	$105.50
Purchase #5	$17.69	3.151%	$18.2474	$18.25	$18.25	$18.20
Purchase #6	$110.90	12.124%	$124.3455	$124.35	$124.35	$124.30
Purchase #7	$18.59	4.475%	$19.4219	$19.42	$19.40	$19.40
7 purchase totals =	$612.32		$659.0529	$659.06	$659.00	$659.00