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	$25.26	11.196%	$28.0881	$28.09	$28.10	$28.10
Purchase #2	$97.78	13.520%	$110.9999	$111.00	$111.00	$111.00
Purchase #3	$95.68	7.748%	$103.0933	$103.09	$103.10	$103.10
Purchase #4	$180.62	12.727%	$203.6075	$203.61	$203.60	$203.60
Purchase #5	$55.79	12.748%	$62.9021	$62.90	$62.90	$62.90
Purchase #6	$138.87	3.150%	$143.2444	$143.24	$143.25	$143.20
Purchase #7	$63.82	12.551%	$71.83	$71.83	$71.85	$71.80
7 purchase totals =	$657.82		$723.7653	$723.76	$723.80	$723.70