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	$249.60	12.570%	$280.9747	$280.97	$280.95	$281.00
Purchase #2	$50.35	4.217%	$52.4733	$52.47	$52.45	$52.50
Purchase #3	$250.94	13.639%	$285.1657	$285.17	$285.15	$285.20
Purchase #4	$54.46	11.799%	$60.8857	$60.89	$60.90	$60.90
Purchase #5	$22.91	3.195%	$23.642	$23.64	$23.65	$23.60
Purchase #6	$243.26	9.669%	$266.7808	$266.78	$266.80	$266.80
Purchase #7	$59.25	4.475%	$61.9014	$61.90	$61.90	$61.90
7 purchase totals =	$930.77		$1,031.8236	$1,031.82	$1,031.80	$1,031.90