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	$239.69	7.147%	$256.8206	$256.82	$256.80	$256.80
Purchase #2	$137.60	9.353%	$150.4697	$150.47	$150.45	$150.50
Purchase #3	$108.73	4.111%	$113.1999	$113.20	$113.20	$113.20
Purchase #4	$21.32	11.873%	$23.8513	$23.85	$23.85	$23.90
Purchase #5	$130.30	9.608%	$142.8192	$142.82	$142.80	$142.80
Purchase #6	$56.64	6.205%	$60.1545	$60.15	$60.15	$60.20
Purchase #7	$66.54	5.626%	$70.2835	$70.28	$70.30	$70.30
7 purchase totals =	$760.82		$817.5987	$817.59	$817.55	$817.70