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	$173.66	9.573%	$190.2845	$190.28	$190.30	$190.30
Purchase #2	$30.80	8.525%	$33.4257	$33.43	$33.45	$33.40
Purchase #3	$143.84	10.873%	$159.4797	$159.48	$159.50	$159.50
Purchase #4	$190.30	4.291%	$198.4658	$198.47	$198.45	$198.50
Purchase #5	$13.36	4.298%	$13.9342	$13.93	$13.95	$13.90
Purchase #6	$242.87	13.330%	$275.2446	$275.24	$275.25	$275.20
Purchase #7	$104.87	4.127%	$109.198	$109.20	$109.20	$109.20
7 purchase totals =	$899.70		$980.0325	$980.03	$980.10	$980.00