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	$200.40	13.222%	$226.8969	$226.90	$226.90	$226.90
Purchase #2	$158.68	12.698%	$178.8292	$178.83	$178.85	$178.80
Purchase #3	$232.60	9.874%	$255.5669	$255.57	$255.55	$255.60
Purchase #4	$200.88	10.576%	$222.1251	$222.13	$222.15	$222.10
Purchase #5	$81.89	5.352%	$86.2728	$86.27	$86.25	$86.30
Purchase #6	$8.88	5.622%	$9.3792	$9.38	$9.40	$9.40
Purchase #7	$217.64	4.219%	$226.8222	$226.82	$226.80	$226.80
7 purchase totals =	$1,100.97		$1,205.8923	$1,205.90	$1,205.90	$1,205.90