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	$63.93	3.450%	$66.1356	$66.14	$66.15	$66.10
Purchase #2	$182.76	12.189%	$205.0366	$205.04	$205.05	$205.00
Purchase #3	$90.29	4.435%	$94.2944	$94.29	$94.30	$94.30
Purchase #4	$6.33	13.337%	$7.1742	$7.17	$7.15	$7.20
Purchase #5	$99.60	8.724%	$108.2891	$108.29	$108.30	$108.30
Purchase #6	$42.44	11.454%	$47.3011	$47.30	$47.30	$47.30
Purchase #7	$39.30	7.772%	$42.3544	$42.35	$42.35	$42.40
7 purchase totals =	$524.65		$570.5854	$570.58	$570.60	$570.60