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	$6.45	13.772%	$7.3383	$7.34	$7.35	$7.30
Purchase #2	$185.74	13.294%	$210.4323	$210.43	$210.45	$210.40
Purchase #3	$107.26	3.737%	$111.2683	$111.27	$111.25	$111.30
Purchase #4	$33.31	4.859%	$34.9285	$34.93	$34.95	$34.90
Purchase #5	$137.94	8.388%	$149.5104	$149.51	$149.50	$149.50
Purchase #6	$141.92	11.690%	$158.5104	$158.51	$158.50	$158.50
Purchase #7	$143.97	4.577%	$150.5595	$150.56	$150.55	$150.60
7 purchase totals =	$756.59		$822.5477	$822.55	$822.55	$822.50