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	$61.44	11.550%	$68.5363	$68.54	$68.55	$68.50
Purchase #2	$126.63	12.733%	$142.7538	$142.75	$142.75	$142.80
Purchase #3	$228.91	9.679%	$251.0662	$251.07	$251.05	$251.10
Purchase #4	$69.49	12.250%	$78.0025	$78.00	$78.00	$78.00
Purchase #5	$91.41	8.868%	$99.5162	$99.52	$99.50	$99.50
Purchase #6	$135.48	4.177%	$141.139	$141.14	$141.15	$141.10
Purchase #7	$47.72	13.748%	$54.2805	$54.28	$54.30	$54.30
7 purchase totals =	$761.08		$835.2945	$835.30	$835.30	$835.30