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	$220.33	12.222%	$247.2587	$247.26	$247.25	$247.30
Purchase #2	$86.98	10.262%	$95.9059	$95.91	$95.90	$95.90
Purchase #3	$74.87	10.212%	$82.5157	$82.52	$82.50	$82.50
Purchase #4	$123.99	5.466%	$130.7673	$130.77	$130.75	$130.80
Purchase #5	$95.93	4.505%	$100.2516	$100.25	$100.25	$100.30
Purchase #6	$141.33	12.440%	$158.9115	$158.91	$158.90	$158.90
Purchase #7	$235.53	8.795%	$256.2449	$256.24	$256.25	$256.20
7 purchase totals =	$978.96		$1,071.8556	$1,071.86	$1,071.80	$1,071.90