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	$40.63	3.461%	$42.0362	$42.04	$42.05	$42.00
Purchase #2	$166.57	12.617%	$187.5861	$187.59	$187.60	$187.60
Purchase #3	$228.73	12.683%	$257.7398	$257.74	$257.75	$257.70
Purchase #4	$138.35	12.228%	$155.2674	$155.27	$155.25	$155.30
Purchase #5	$228.56	13.823%	$260.1538	$260.15	$260.15	$260.20
Purchase #6	$130.86	13.807%	$148.9278	$148.93	$148.95	$148.90
Purchase #7	$234.87	9.255%	$256.6072	$256.61	$256.60	$256.60
7 purchase totals =	$1,168.57		$1,308.3183	$1,308.33	$1,308.35	$1,308.30