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	$139.63	13.261%	$158.1463	$158.15	$158.15	$158.10
Purchase #2	$121.85	4.409%	$127.2224	$127.22	$127.20	$127.20
Purchase #3	$190.80	13.406%	$216.3786	$216.38	$216.40	$216.40
Purchase #4	$29.78	9.561%	$32.6273	$32.63	$32.65	$32.60
Purchase #5	$224.93	11.759%	$251.3795	$251.38	$251.40	$251.40
Purchase #6	$70.94	11.451%	$79.0633	$79.06	$79.05	$79.10
Purchase #7	$128.49	7.298%	$137.8672	$137.87	$137.85	$137.90
7 purchase totals =	$906.42		$1,002.6846	$1,002.69	$1,002.70	$1,002.70