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	$89.46	3.824%	$92.881	$92.88	$92.90	$92.90
Purchase #2	$84.45	11.475%	$94.1406	$94.14	$94.15	$94.10
Purchase #3	$25.84	6.164%	$27.4328	$27.43	$27.45	$27.40
Purchase #4	$183.88	9.280%	$200.9441	$200.94	$200.95	$200.90
Purchase #5	$187.52	9.489%	$205.3138	$205.31	$205.30	$205.30
Purchase #6	$38.81	8.297%	$42.0301	$42.03	$42.05	$42.00
Purchase #7	$133.41	10.509%	$147.4301	$147.43	$147.45	$147.40
7 purchase totals =	$743.37		$810.1725	$810.16	$810.25	$810.00