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	$152.50	13.126%	$172.5172	$172.52	$172.50	$172.50
Purchase #2	$176.98	7.519%	$190.2871	$190.29	$190.30	$190.30
Purchase #3	$49.66	12.624%	$55.9291	$55.93	$55.95	$55.90
Purchase #4	$41.82	10.613%	$46.2584	$46.26	$46.25	$46.30
Purchase #5	$93.50	7.580%	$100.5873	$100.59	$100.60	$100.60
Purchase #6	$243.30	7.166%	$260.7349	$260.73	$260.75	$260.70
Purchase #7	$11.87	8.279%	$12.8527	$12.85	$12.85	$12.90
7 purchase totals =	$769.63		$839.1667	$839.17	$839.20	$839.20