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	$138.93	10.766%	$153.8872	$153.89	$153.90	$153.90
Purchase #2	$245.80	9.431%	$268.9814	$268.98	$269.00	$269.00
Purchase #3	$122.86	6.660%	$131.0425	$131.04	$131.05	$131.00
Purchase #4	$126.85	10.208%	$139.7988	$139.80	$139.80	$139.80
Purchase #5	$137.83	4.243%	$143.6781	$143.68	$143.70	$143.70
Purchase #6	$128.51	7.746%	$138.4644	$138.46	$138.45	$138.50
Purchase #7	$158.50	4.637%	$165.8496	$165.85	$165.85	$165.80
7 purchase totals =	$1,059.28		$1,141.7020	$1,141.70	$1,141.75	$1,141.70