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	$205.41	7.783%	$221.3971	$221.40	$221.40	$221.40
Purchase #2	$241.32	3.113%	$248.8323	$248.83	$248.85	$248.80
Purchase #3	$21.95	12.104%	$24.6068	$24.61	$24.60	$24.60
Purchase #4	$50.30	10.301%	$55.4814	$55.48	$55.50	$55.50
Purchase #5	$222.72	13.845%	$253.5556	$253.56	$253.55	$253.60
Purchase #6	$139.79	12.592%	$157.3924	$157.39	$157.40	$157.40
Purchase #7	$223.91	13.657%	$254.4894	$254.49	$254.50	$254.50
7 purchase totals =	$1,105.40		$1,215.7550	$1,215.76	$1,215.80	$1,215.80