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	$23.37	4.634%	$24.453	$24.45	$24.45	$24.50
Purchase #2	$220.62	3.219%	$227.7218	$227.72	$227.70	$227.70
Purchase #3	$9.29	9.112%	$10.1365	$10.14	$10.15	$10.10
Purchase #4	$54.90	8.497%	$59.5649	$59.56	$59.55	$59.60
Purchase #5	$243.50	5.363%	$256.5589	$256.56	$256.55	$256.60
Purchase #6	$139.65	13.111%	$157.9595	$157.96	$157.95	$158.00
Purchase #7	$83.59	4.635%	$87.4644	$87.46	$87.45	$87.50
7 purchase totals =	$774.92		$823.8590	$823.85	$823.80	$824.00