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	$127.28	8.291%	$137.8328	$137.83	$137.85	$137.80
Purchase #2	$108.70	3.304%	$112.2914	$112.29	$112.30	$112.30
Purchase #3	$108.27	13.198%	$122.5595	$122.56	$122.55	$122.60
Purchase #4	$248.64	12.234%	$279.0586	$279.06	$279.05	$279.10
Purchase #5	$250.72	5.845%	$265.3746	$265.37	$265.35	$265.40
Purchase #6	$144.74	7.678%	$155.8531	$155.85	$155.85	$155.90
Purchase #7	$103.84	5.503%	$109.5543	$109.55	$109.55	$109.60
7 purchase totals =	$1,092.19		$1,182.5243	$1,182.51	$1,182.50	$1,182.70