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	$103.85	4.286%	$108.301	$108.30	$108.30	$108.30
Purchase #2	$81.58	10.113%	$89.8302	$89.83	$89.85	$89.80
Purchase #3	$101.44	4.203%	$105.7035	$105.70	$105.70	$105.70
Purchase #4	$31.36	8.189%	$33.9281	$33.93	$33.95	$33.90
Purchase #5	$124.49	13.854%	$141.7368	$141.74	$141.75	$141.70
Purchase #6	$24.72	12.579%	$27.8295	$27.83	$27.85	$27.80
Purchase #7	$46.74	10.736%	$51.758	$51.76	$51.75	$51.80
7 purchase totals =	$514.18		$559.0871	$559.09	$559.15	$559.00