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	$17.42	6.384%	$18.5321	$18.53	$18.55	$18.50
Purchase #2	$52.82	12.156%	$59.2408	$59.24	$59.25	$59.20
Purchase #3	$103.66	8.796%	$112.7779	$112.78	$112.80	$112.80
Purchase #4	$81.73	8.700%	$88.8405	$88.84	$88.85	$88.80
Purchase #5	$166.71	6.105%	$176.8876	$176.89	$176.90	$176.90
Purchase #6	$230.93	9.275%	$252.3488	$252.35	$252.35	$252.30
Purchase #7	$85.67	4.781%	$89.7659	$89.77	$89.75	$89.80
7 purchase totals =	$738.94		$798.3936	$798.40	$798.45	$798.30