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	$60.78	13.301%	$68.8643	$68.86	$68.85	$68.90
Purchase #2	$65.41	10.286%	$72.1381	$72.14	$72.15	$72.10
Purchase #3	$35.42	13.321%	$40.1383	$40.14	$40.15	$40.10
Purchase #4	$148.35	3.208%	$153.1091	$153.11	$153.10	$153.10
Purchase #5	$86.84	3.124%	$89.5529	$89.55	$89.55	$89.60
Purchase #6	$196.61	13.262%	$222.6844	$222.68	$222.70	$222.70
Purchase #7	$194.99	7.426%	$209.47	$209.47	$209.45	$209.50
7 purchase totals =	$788.40		$855.9571	$855.95	$855.95	$856.00