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	$226.28	13.675%	$257.2238	$257.22	$257.20	$257.20
Purchase #2	$82.43	9.533%	$90.2881	$90.29	$90.30	$90.30
Purchase #3	$57.44	4.322%	$59.9226	$59.92	$59.90	$59.90
Purchase #4	$173.60	10.178%	$191.269	$191.27	$191.25	$191.30
Purchase #5	$68.88	5.276%	$72.5141	$72.51	$72.50	$72.50
Purchase #6	$13.49	6.561%	$14.3751	$14.38	$14.40	$14.40
Purchase #7	$206.70	11.372%	$230.2059	$230.21	$230.20	$230.20
7 purchase totals =	$828.82		$915.7986	$915.80	$915.75	$915.80