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	$95.71	9.143%	$104.4608	$104.46	$104.45	$104.50
Purchase #2	$129.88	10.435%	$143.433	$143.43	$143.45	$143.40
Purchase #3	$45.70	6.653%	$48.7404	$48.74	$48.75	$48.70
Purchase #4	$156.54	5.463%	$165.0918	$165.09	$165.10	$165.10
Purchase #5	$124.67	5.481%	$131.5032	$131.50	$131.50	$131.50
Purchase #6	$128.86	13.541%	$146.3089	$146.31	$146.30	$146.30
Purchase #7	$178.80	11.537%	$199.4282	$199.43	$199.45	$199.40
7 purchase totals =	$860.16		$938.9663	$938.96	$939.00	$938.90