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	$11.84	11.217%	$13.1681	$13.17	$13.15	$13.20
Purchase #2	$36.28	4.324%	$37.8487	$37.85	$37.85	$37.80
Purchase #3	$44.60	10.463%	$49.2665	$49.27	$49.25	$49.30
Purchase #4	$206.54	5.314%	$217.5155	$217.52	$217.50	$217.50
Purchase #5	$199.69	9.455%	$218.5707	$218.57	$218.55	$218.60
Purchase #6	$82.98	10.149%	$91.4016	$91.40	$91.40	$91.40
Purchase #7	$172.35	4.229%	$179.6387	$179.64	$179.65	$179.60
7 purchase totals =	$754.28		$807.4098	$807.42	$807.35	$807.40