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	$243.28	4.262%	$253.6486	$253.65	$253.65	$253.60
Purchase #2	$117.48	4.793%	$123.1108	$123.11	$123.10	$123.10
Purchase #3	$118.96	3.725%	$123.3913	$123.39	$123.40	$123.40
Purchase #4	$58.82	13.690%	$66.8725	$66.87	$66.85	$66.90
Purchase #5	$184.42	11.388%	$205.4217	$205.42	$205.40	$205.40
Purchase #6	$230.51	12.715%	$259.8193	$259.82	$259.80	$259.80
Purchase #7	$127.32	12.624%	$143.3929	$143.39	$143.40	$143.40
7 purchase totals =	$1,080.79		$1,175.6571	$1,175.65	$1,175.60	$1,175.60