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	$103.39	8.483%	$112.1606	$112.16	$112.15	$112.20
Purchase #2	$66.77	6.831%	$71.3311	$71.33	$71.35	$71.30
Purchase #3	$238.37	12.852%	$269.0053	$269.01	$269.00	$269.00
Purchase #4	$247.59	8.856%	$269.5166	$269.52	$269.50	$269.50
Purchase #5	$190.31	13.162%	$215.3586	$215.36	$215.35	$215.40
Purchase #6	$130.56	5.309%	$137.4914	$137.49	$137.50	$137.50
Purchase #7	$36.71	10.159%	$40.4394	$40.44	$40.45	$40.40
7 purchase totals =	$1,013.70		$1,115.3030	$1,115.31	$1,115.30	$1,115.30