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	$42.78	5.753%	$45.2411	$45.24	$45.25	$45.20
Purchase #2	$135.60	5.282%	$142.7624	$142.76	$142.75	$142.80
Purchase #3	$130.82	10.780%	$144.9224	$144.92	$144.90	$144.90
Purchase #4	$108.36	4.758%	$113.5158	$113.52	$113.50	$113.50
Purchase #5	$55.30	11.149%	$61.4654	$61.47	$61.45	$61.50
Purchase #6	$154.43	10.249%	$170.2575	$170.26	$170.25	$170.30
Purchase #7	$34.81	11.376%	$38.77	$38.77	$38.75	$38.80
7 purchase totals =	$662.10		$716.9346	$716.94	$716.85	$717.00