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	$149.28	10.204%	$164.5125	$164.51	$164.50	$164.50
Purchase #2	$136.73	5.662%	$144.4717	$144.47	$144.45	$144.50
Purchase #3	$225.61	12.800%	$254.4881	$254.49	$254.50	$254.50
Purchase #4	$172.43	3.771%	$178.9323	$178.93	$178.95	$178.90
Purchase #5	$111.74	8.151%	$120.8479	$120.85	$120.85	$120.80
Purchase #6	$86.46	10.837%	$95.8297	$95.83	$95.85	$95.80
Purchase #7	$19.31	8.478%	$20.9471	$20.95	$20.95	$20.90
7 purchase totals =	$901.56		$980.0293	$980.03	$980.05	$979.90