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	$13.40	12.668%	$15.0975	$15.10	$15.10	$15.10
Purchase #2	$81.32	11.288%	$90.4994	$90.50	$90.50	$90.50
Purchase #3	$236.66	9.383%	$258.8658	$258.87	$258.85	$258.90
Purchase #4	$143.51	11.547%	$160.0811	$160.08	$160.10	$160.10
Purchase #5	$65.82	13.729%	$74.8564	$74.86	$74.85	$74.90
Purchase #6	$80.47	13.842%	$91.6087	$91.61	$91.60	$91.60
Purchase #7	$35.77	9.536%	$39.181	$39.18	$39.20	$39.20
7 purchase totals =	$656.95		$730.1899	$730.20	$730.20	$730.30