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	$238.88	13.494%	$271.1145	$271.11	$271.10	$271.10
Purchase #2	$137.94	5.519%	$145.5529	$145.55	$145.55	$145.60
Purchase #3	$15.81	13.749%	$17.9837	$17.98	$18.00	$18.00
Purchase #4	$119.37	5.540%	$125.9831	$125.98	$126.00	$126.00
Purchase #5	$12.37	12.614%	$13.9304	$13.93	$13.95	$13.90
Purchase #6	$242.70	13.320%	$275.0276	$275.03	$275.05	$275.00
Purchase #7	$159.89	6.283%	$169.9359	$169.94	$169.95	$169.90
7 purchase totals =	$926.96		$1,019.5281	$1,019.52	$1,019.60	$1,019.50