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	$217.40	6.122%	$230.7092	$230.71	$230.70	$230.70
Purchase #2	$235.40	4.255%	$245.4163	$245.42	$245.40	$245.40
Purchase #3	$38.69	4.487%	$40.426	$40.43	$40.45	$40.40
Purchase #4	$141.75	11.379%	$157.8797	$157.88	$157.90	$157.90
Purchase #5	$146.47	5.810%	$154.9799	$154.98	$155.00	$155.00
Purchase #6	$85.31	4.365%	$89.0338	$89.03	$89.05	$89.00
Purchase #7	$150.79	13.371%	$170.9521	$170.95	$170.95	$171.00
7 purchase totals =	$1,015.81		$1,089.3970	$1,089.40	$1,089.45	$1,089.40