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	$154.72	3.795%	$160.5916	$160.59	$160.60	$160.60
Purchase #2	$128.78	8.354%	$139.5383	$139.54	$139.55	$139.50
Purchase #3	$136.98	3.360%	$141.5825	$141.58	$141.60	$141.60
Purchase #4	$72.75	11.323%	$80.9875	$80.99	$81.00	$81.00
Purchase #5	$103.48	7.545%	$111.2876	$111.29	$111.30	$111.30
Purchase #6	$95.33	11.136%	$105.9459	$105.95	$105.95	$105.90
Purchase #7	$54.63	12.466%	$61.4402	$61.44	$61.45	$61.40
7 purchase totals =	$746.67		$801.3736	$801.38	$801.45	$801.30