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	$18.31	7.828%	$19.7433	$19.74	$19.75	$19.70
Purchase #2	$98.46	13.129%	$111.3868	$111.39	$111.40	$111.40
Purchase #3	$206.63	13.536%	$234.5994	$234.60	$234.60	$234.60
Purchase #4	$52.95	6.373%	$56.3245	$56.32	$56.30	$56.30
Purchase #5	$162.71	5.608%	$171.8348	$171.83	$171.85	$171.80
Purchase #6	$159.35	7.597%	$171.4558	$171.46	$171.45	$171.50
Purchase #7	$168.65	4.735%	$176.6356	$176.64	$176.65	$176.60
7 purchase totals =	$867.06		$941.9802	$941.98	$942.00	$941.90