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	$93.85	5.543%	$99.0521	$99.05	$99.05	$99.10
Purchase #2	$81.27	9.531%	$89.0158	$89.02	$89.00	$89.00
Purchase #3	$232.99	10.820%	$258.1995	$258.20	$258.20	$258.20
Purchase #4	$102.31	13.466%	$116.0871	$116.09	$116.10	$116.10
Purchase #5	$104.97	6.418%	$111.707	$111.71	$111.70	$111.70
Purchase #6	$158.84	6.775%	$169.6014	$169.60	$169.60	$169.60
Purchase #7	$58.97	6.428%	$62.7606	$62.76	$62.75	$62.80
7 purchase totals =	$833.20		$906.4235	$906.43	$906.40	$906.50