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	$193.55	6.134%	$205.4224	$205.42	$205.40	$205.40
Purchase #2	$13.43	11.510%	$14.9758	$14.98	$15.00	$15.00
Purchase #3	$233.96	11.627%	$261.1625	$261.16	$261.15	$261.20
Purchase #4	$177.60	12.599%	$199.9758	$199.98	$200.00	$200.00
Purchase #5	$111.36	4.750%	$116.6496	$116.65	$116.65	$116.60
Purchase #6	$197.71	12.304%	$222.0362	$222.04	$222.05	$222.00
Purchase #7	$248.27	12.719%	$279.8475	$279.85	$279.85	$279.80
7 purchase totals =	$1,175.88		$1,300.0698	$1,300.08	$1,300.10	$1,300.00