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	$19.52	9.842%	$21.4412	$21.44	$21.45	$21.40
Purchase #2	$46.60	10.554%	$51.5182	$51.52	$51.50	$51.50
Purchase #3	$50.78	10.109%	$55.9134	$55.91	$55.90	$55.90
Purchase #4	$232.83	7.249%	$249.7078	$249.71	$249.70	$249.70
Purchase #5	$62.63	5.349%	$65.9801	$65.98	$66.00	$66.00
Purchase #6	$177.51	10.546%	$196.2302	$196.23	$196.25	$196.20
Purchase #7	$234.86	9.309%	$256.7231	$256.72	$256.70	$256.70
7 purchase totals =	$824.73		$897.5140	$897.51	$897.50	$897.40