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	$104.57	12.294%	$117.4258	$117.43	$117.45	$117.40
Purchase #2	$106.59	10.114%	$117.3705	$117.37	$117.35	$117.40
Purchase #3	$166.46	11.611%	$185.7877	$185.79	$185.80	$185.80
Purchase #4	$38.26	12.331%	$42.9778	$42.98	$43.00	$43.00
Purchase #5	$41.83	10.553%	$46.2443	$46.24	$46.25	$46.20
Purchase #6	$99.82	3.618%	$103.4315	$103.43	$103.45	$103.40
Purchase #7	$22.58	4.578%	$23.6137	$23.61	$23.60	$23.60
7 purchase totals =	$580.11		$636.8513	$636.85	$636.90	$636.80