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	$17.84	5.505%	$18.8221	$18.82	$18.80	$18.80
Purchase #2	$136.59	13.481%	$155.0037	$155.00	$155.00	$155.00
Purchase #3	$184.65	3.170%	$190.5034	$190.50	$190.50	$190.50
Purchase #4	$88.63	3.175%	$91.444	$91.44	$91.45	$91.40
Purchase #5	$66.42	3.177%	$68.5302	$68.53	$68.55	$68.50
Purchase #6	$233.52	10.486%	$258.0069	$258.01	$258.00	$258.00
Purchase #7	$182.48	4.412%	$190.531	$190.53	$190.55	$190.50
7 purchase totals =	$910.13		$972.8413	$972.83	$972.85	$972.70