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	$246.63	11.563%	$275.1478	$275.15	$275.15	$275.10
Purchase #2	$15.52	12.621%	$17.4788	$17.48	$17.50	$17.50
Purchase #3	$62.99	12.340%	$70.763	$70.76	$70.75	$70.80
Purchase #4	$64.53	12.865%	$72.8318	$72.83	$72.85	$72.80
Purchase #5	$96.53	9.631%	$105.8268	$105.83	$105.85	$105.80
Purchase #6	$32.32	7.808%	$34.8435	$34.84	$34.85	$34.80
Purchase #7	$55.31	4.307%	$57.6922	$57.69	$57.70	$57.70
7 purchase totals =	$573.83		$634.5839	$634.58	$634.65	$634.50