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	$66.70	8.609%	$72.4422	$72.44	$72.45	$72.40
Purchase #2	$81.48	11.656%	$90.9773	$90.98	$91.00	$91.00
Purchase #3	$25.70	5.445%	$27.0994	$27.10	$27.10	$27.10
Purchase #4	$115.79	6.747%	$123.6024	$123.60	$123.60	$123.60
Purchase #5	$89.92	4.343%	$93.8252	$93.83	$93.85	$93.80
Purchase #6	$46.43	12.568%	$52.2653	$52.27	$52.25	$52.30
Purchase #7	$122.25	13.281%	$138.486	$138.49	$138.50	$138.50
7 purchase totals =	$548.27		$598.6978	$598.71	$598.75	$598.70