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	$198.76	11.784%	$222.1819	$222.18	$222.20	$222.20
Purchase #2	$222.87	11.509%	$248.5201	$248.52	$248.50	$248.50
Purchase #3	$156.87	8.308%	$169.9028	$169.90	$169.90	$169.90
Purchase #4	$18.58	10.710%	$20.5699	$20.57	$20.55	$20.60
Purchase #5	$115.46	9.856%	$126.8397	$126.84	$126.85	$126.80
Purchase #6	$137.54	3.250%	$142.0101	$142.01	$142.00	$142.00
Purchase #7	$17.97	7.589%	$19.3337	$19.33	$19.35	$19.30
7 purchase totals =	$868.05		$949.3582	$949.35	$949.35	$949.30