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	$11.34	8.362%	$12.2883	$12.29	$12.30	$12.30
Purchase #2	$239.51	11.452%	$266.9387	$266.94	$266.95	$266.90
Purchase #3	$108.37	3.172%	$111.8075	$111.81	$111.80	$111.80
Purchase #4	$72.51	10.870%	$80.3918	$80.39	$80.40	$80.40
Purchase #5	$157.73	11.430%	$175.7585	$175.76	$175.75	$175.80
Purchase #6	$170.43	9.737%	$187.0248	$187.02	$187.00	$187.00
Purchase #7	$131.82	12.459%	$148.2435	$148.24	$148.25	$148.20
7 purchase totals =	$891.71		$982.4531	$982.45	$982.45	$982.40