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	$51.98	4.851%	$54.5015	$54.50	$54.50	$54.50
Purchase #2	$200.56	7.615%	$215.8326	$215.83	$215.85	$215.80
Purchase #3	$166.30	8.136%	$179.8302	$179.83	$179.85	$179.80
Purchase #4	$106.31	5.691%	$112.3601	$112.36	$112.35	$112.40
Purchase #5	$118.86	6.714%	$126.8403	$126.84	$126.85	$126.80
Purchase #6	$46.88	12.406%	$52.6959	$52.70	$52.70	$52.70
Purchase #7	$182.58	3.549%	$189.0598	$189.06	$189.05	$189.10
7 purchase totals =	$873.47		$931.1204	$931.12	$931.15	$931.10