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	$21.60	11.583%	$24.1019	$24.10	$24.10	$24.10
Purchase #2	$103.62	12.483%	$116.5549	$116.55	$116.55	$116.60
Purchase #3	$234.96	7.789%	$253.261	$253.26	$253.25	$253.30
Purchase #4	$240.90	6.120%	$255.6431	$255.64	$255.65	$255.60
Purchase #5	$95.27	10.789%	$105.5487	$105.55	$105.55	$105.50
Purchase #6	$182.87	5.825%	$193.5222	$193.52	$193.50	$193.50
Purchase #7	$77.91	6.140%	$82.6937	$82.69	$82.70	$82.70
7 purchase totals =	$957.13		$1,031.3255	$1,031.31	$1,031.30	$1,031.30