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	$20.75	3.631%	$21.5034	$21.50	$21.50	$21.50
Purchase #2	$183.82	10.814%	$203.6983	$203.70	$203.70	$203.70
Purchase #3	$61.98	4.837%	$64.978	$64.98	$65.00	$65.00
Purchase #4	$99.26	12.258%	$111.4273	$111.43	$111.45	$111.40
Purchase #5	$12.64	9.453%	$13.8349	$13.83	$13.85	$13.80
Purchase #6	$41.61	7.156%	$44.5876	$44.59	$44.60	$44.60
Purchase #7	$226.63	8.871%	$246.7343	$246.73	$246.75	$246.70
7 purchase totals =	$646.69		$706.7638	$706.76	$706.85	$706.70