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	$20.58	3.146%	$21.2274	$21.23	$21.25	$21.20
Purchase #2	$118.75	3.499%	$122.9051	$122.91	$122.90	$122.90
Purchase #3	$63.28	11.449%	$70.5249	$70.52	$70.50	$70.50
Purchase #4	$47.95	12.845%	$54.1092	$54.11	$54.10	$54.10
Purchase #5	$86.84	4.626%	$90.8572	$90.86	$90.85	$90.90
Purchase #6	$44.45	6.104%	$47.1632	$47.16	$47.15	$47.20
Purchase #7	$132.83	8.579%	$144.2255	$144.23	$144.25	$144.20
7 purchase totals =	$514.68		$551.0125	$551.02	$551.00	$551.00