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	$218.87	6.716%	$233.5693	$233.57	$233.55	$233.60
Purchase #2	$178.69	4.572%	$186.8597	$186.86	$186.85	$186.90
Purchase #3	$105.31	11.841%	$117.7798	$117.78	$117.80	$117.80
Purchase #4	$72.78	5.493%	$76.7778	$76.78	$76.80	$76.80
Purchase #5	$238.51	13.147%	$269.8669	$269.87	$269.85	$269.90
Purchase #6	$20.70	13.465%	$23.4873	$23.49	$23.50	$23.50
Purchase #7	$159.56	7.801%	$172.0073	$172.01	$172.00	$172.00
7 purchase totals =	$994.42		$1,080.3481	$1,080.36	$1,080.35	$1,080.50