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	$91.38	13.456%	$103.6761	$103.68	$103.70	$103.70
Purchase #2	$229.90	9.809%	$252.4509	$252.45	$252.45	$252.50
Purchase #3	$55.31	12.250%	$62.0855	$62.09	$62.10	$62.10
Purchase #4	$120.48	4.592%	$126.0124	$126.01	$126.00	$126.00
Purchase #5	$72.35	5.641%	$76.4313	$76.43	$76.45	$76.40
Purchase #6	$117.73	8.508%	$127.7465	$127.75	$127.75	$127.70
Purchase #7	$150.55	10.170%	$165.8609	$165.86	$165.85	$165.90
7 purchase totals =	$837.70		$914.2636	$914.27	$914.30	$914.30