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	$139.71	8.403%	$151.4498	$151.45	$151.45	$151.40
Purchase #2	$16.83	6.136%	$17.8627	$17.86	$17.85	$17.90
Purchase #3	$102.97	8.125%	$111.3363	$111.34	$111.35	$111.30
Purchase #4	$131.63	12.583%	$148.193	$148.19	$148.20	$148.20
Purchase #5	$62.73	7.661%	$67.5357	$67.54	$67.55	$67.50
Purchase #6	$39.77	9.527%	$43.5589	$43.56	$43.55	$43.60
Purchase #7	$92.36	13.335%	$104.6762	$104.68	$104.70	$104.70
7 purchase totals =	$586.00		$644.6126	$644.62	$644.65	$644.60