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	$102.88	12.828%	$116.0774	$116.08	$116.10	$116.10
Purchase #2	$190.59	9.144%	$208.0175	$208.02	$208.00	$208.00
Purchase #3	$250.69	10.436%	$276.852	$276.85	$276.85	$276.90
Purchase #4	$13.97	12.510%	$15.7176	$15.72	$15.70	$15.70
Purchase #5	$99.97	11.377%	$111.3436	$111.34	$111.35	$111.30
Purchase #6	$118.74	7.160%	$127.2418	$127.24	$127.25	$127.20
Purchase #7	$214.72	13.359%	$243.4044	$243.40	$243.40	$243.40
7 purchase totals =	$991.56		$1,098.6543	$1,098.65	$1,098.65	$1,098.60