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	$139.51	12.112%	$156.4075	$156.41	$156.40	$156.40
Purchase #2	$18.47	5.473%	$19.4809	$19.48	$19.50	$19.50
Purchase #3	$126.43	8.842%	$137.6089	$137.61	$137.60	$137.60
Purchase #4	$91.84	9.244%	$100.3297	$100.33	$100.35	$100.30
Purchase #5	$94.56	11.203%	$105.1536	$105.15	$105.15	$105.20
Purchase #6	$231.82	10.105%	$255.2454	$255.25	$255.25	$255.20
Purchase #7	$208.96	4.347%	$218.0435	$218.04	$218.05	$218.00
7 purchase totals =	$911.59		$992.2695	$992.27	$992.30	$992.20