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	$120.53	10.103%	$132.7071	$132.71	$132.70	$132.70
Purchase #2	$70.58	3.290%	$72.9021	$72.90	$72.90	$72.90
Purchase #3	$56.46	9.410%	$61.7729	$61.77	$61.75	$61.80
Purchase #4	$70.98	4.307%	$74.0371	$74.04	$74.05	$74.00
Purchase #5	$93.26	7.561%	$100.3114	$100.31	$100.30	$100.30
Purchase #6	$81.81	10.592%	$90.4753	$90.48	$90.50	$90.50
Purchase #7	$248.59	12.810%	$280.4344	$280.43	$280.45	$280.40
7 purchase totals =	$742.21		$812.6403	$812.64	$812.65	$812.60