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	$245.81	8.531%	$266.7801	$266.78	$266.80	$266.80
Purchase #2	$59.38	11.681%	$66.3162	$66.32	$66.30	$66.30
Purchase #3	$180.41	4.529%	$188.5808	$188.58	$188.60	$188.60
Purchase #4	$128.43	8.845%	$139.7896	$139.79	$139.80	$139.80
Purchase #5	$86.63	3.240%	$89.4368	$89.44	$89.45	$89.40
Purchase #6	$10.87	5.236%	$11.4392	$11.44	$11.45	$11.40
Purchase #7	$88.77	13.471%	$100.7282	$100.73	$100.75	$100.70
7 purchase totals =	$800.30		$863.0709	$863.08	$863.15	$863.00