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	$102.71	9.728%	$112.7016	$112.70	$112.70	$112.70
Purchase #2	$128.32	3.227%	$132.4609	$132.46	$132.45	$132.50
Purchase #3	$207.56	12.488%	$233.4801	$233.48	$233.50	$233.50
Purchase #4	$56.55	4.409%	$59.0433	$59.04	$59.05	$59.00
Purchase #5	$12.34	10.649%	$13.6541	$13.65	$13.65	$13.70
Purchase #6	$248.62	7.510%	$267.2914	$267.29	$267.30	$267.30
Purchase #7	$93.57	7.834%	$100.9003	$100.90	$100.90	$100.90
7 purchase totals =	$849.67		$919.5317	$919.52	$919.55	$919.60