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	$36.43	10.848%	$40.3819	$40.38	$40.40	$40.40
Purchase #2	$100.70	11.540%	$112.3208	$112.32	$112.30	$112.30
Purchase #3	$243.71	11.247%	$271.1201	$271.12	$271.10	$271.10
Purchase #4	$32.94	3.322%	$34.0343	$34.03	$34.05	$34.00
Purchase #5	$68.83	12.253%	$77.2637	$77.26	$77.25	$77.30
Purchase #6	$86.72	6.621%	$92.4617	$92.46	$92.45	$92.50
Purchase #7	$93.75	5.455%	$98.8641	$98.86	$98.85	$98.90
7 purchase totals =	$663.08		$726.4466	$726.43	$726.40	$726.50