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	$50.53	10.218%	$55.6932	$55.69	$55.70	$55.70
Purchase #2	$119.76	9.537%	$131.1815	$131.18	$131.20	$131.20
Purchase #3	$69.28	5.208%	$72.8881	$72.89	$72.90	$72.90
Purchase #4	$13.94	12.453%	$15.6759	$15.68	$15.70	$15.70
Purchase #5	$132.87	11.654%	$148.3547	$148.35	$148.35	$148.40
Purchase #6	$50.98	4.253%	$53.1482	$53.15	$53.15	$53.10
Purchase #7	$198.39	6.434%	$211.1544	$211.15	$211.15	$211.20
7 purchase totals =	$635.75		$688.0960	$688.09	$688.15	$688.20