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	$161.79	13.414%	$183.4925	$183.49	$183.50	$183.50
Purchase #2	$180.56	8.770%	$196.3951	$196.40	$196.40	$196.40
Purchase #3	$207.57	13.614%	$235.8286	$235.83	$235.85	$235.80
Purchase #4	$12.47	7.622%	$13.4205	$13.42	$13.40	$13.40
Purchase #5	$200.78	8.733%	$218.3141	$218.31	$218.30	$218.30
Purchase #6	$181.78	10.521%	$200.9051	$200.91	$200.90	$200.90
Purchase #7	$102.75	10.552%	$113.5922	$113.59	$113.60	$113.60
7 purchase totals =	$1,047.70		$1,161.9481	$1,161.95	$1,161.95	$1,161.90