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	$71.28	5.396%	$75.1263	$75.13	$75.15	$75.10
Purchase #2	$184.44	8.141%	$199.4553	$199.46	$199.45	$199.50
Purchase #3	$149.82	9.701%	$164.354	$164.35	$164.35	$164.40
Purchase #4	$135.83	7.509%	$146.0295	$146.03	$146.05	$146.00
Purchase #5	$111.51	10.779%	$123.5297	$123.53	$123.55	$123.50
Purchase #6	$178.68	11.426%	$199.096	$199.10	$199.10	$199.10
Purchase #7	$63.37	11.357%	$70.5669	$70.57	$70.55	$70.60
7 purchase totals =	$894.93		$978.1577	$978.17	$978.20	$978.20