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	$44.69	12.433%	$50.2463	$50.25	$50.25	$50.20
Purchase #2	$100.34	11.440%	$111.8189	$111.82	$111.80	$111.80
Purchase #3	$117.66	12.388%	$132.2357	$132.24	$132.25	$132.20
Purchase #4	$15.60	3.521%	$16.1493	$16.15	$16.15	$16.10
Purchase #5	$174.67	3.841%	$181.3791	$181.38	$181.40	$181.40
Purchase #6	$80.73	6.627%	$86.08	$86.08	$86.10	$86.10
Purchase #7	$66.70	9.235%	$72.8597	$72.86	$72.85	$72.90
7 purchase totals =	$600.39		$650.7690	$650.78	$650.80	$650.70