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	$61.86	3.451%	$63.9948	$63.99	$64.00	$64.00
Purchase #2	$248.43	12.171%	$278.6664	$278.67	$278.65	$278.70
Purchase #3	$250.90	8.746%	$272.8437	$272.84	$272.85	$272.80
Purchase #4	$75.57	3.520%	$78.2301	$78.23	$78.25	$78.20
Purchase #5	$69.83	3.301%	$72.1351	$72.14	$72.15	$72.10
Purchase #6	$227.92	12.203%	$255.7331	$255.73	$255.75	$255.70
Purchase #7	$57.78	13.363%	$65.5011	$65.50	$65.50	$65.50
7 purchase totals =	$992.29		$1,087.1043	$1,087.10	$1,087.15	$1,087.00