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	$33.45	5.469%	$35.2794	$35.28	$35.30	$35.30
Purchase #2	$143.58	4.836%	$150.5235	$150.52	$150.50	$150.50
Purchase #3	$201.92	13.291%	$228.7572	$228.76	$228.75	$228.80
Purchase #4	$38.61	9.122%	$42.132	$42.13	$42.15	$42.10
Purchase #5	$235.61	8.861%	$256.4874	$256.49	$256.50	$256.50
Purchase #6	$51.66	8.443%	$56.0217	$56.02	$56.00	$56.00
Purchase #7	$201.67	3.534%	$208.797	$208.80	$208.80	$208.80
7 purchase totals =	$906.50		$977.9982	$978.00	$978.00	$978.00