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	$21.91	12.431%	$24.6336	$24.63	$24.65	$24.60
Purchase #2	$53.26	9.847%	$58.5045	$58.50	$58.50	$58.50
Purchase #3	$95.46	3.187%	$98.5023	$98.50	$98.50	$98.50
Purchase #4	$114.59	3.492%	$118.5915	$118.59	$118.60	$118.60
Purchase #5	$243.94	9.197%	$266.3752	$266.38	$266.40	$266.40
Purchase #6	$31.28	10.433%	$34.5434	$34.54	$34.55	$34.50
Purchase #7	$51.63	6.309%	$54.8873	$54.89	$54.90	$54.90
7 purchase totals =	$612.07		$656.0378	$656.03	$656.10	$656.00