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	$226.35	13.803%	$257.5931	$257.59	$257.60	$257.60
Purchase #2	$19.35	5.577%	$20.4291	$20.43	$20.45	$20.40
Purchase #3	$205.25	7.173%	$219.9726	$219.97	$219.95	$220.00
Purchase #4	$115.58	6.616%	$123.2268	$123.23	$123.25	$123.20
Purchase #5	$241.72	8.547%	$262.3798	$262.38	$262.40	$262.40
Purchase #6	$99.69	12.758%	$112.4085	$112.41	$112.40	$112.40
Purchase #7	$41.73	11.248%	$46.4238	$46.42	$46.40	$46.40
7 purchase totals =	$949.67		$1,042.4337	$1,042.43	$1,042.45	$1,042.40