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	$181.40	13.187%	$205.3212	$205.32	$205.30	$205.30
Purchase #2	$82.62	7.592%	$88.8925	$88.89	$88.90	$88.90
Purchase #3	$118.91	3.748%	$123.3667	$123.37	$123.35	$123.40
Purchase #4	$10.39	4.451%	$10.8525	$10.85	$10.85	$10.90
Purchase #5	$118.29	7.772%	$127.4835	$127.48	$127.50	$127.50
Purchase #6	$142.39	12.360%	$159.9894	$159.99	$160.00	$160.00
Purchase #7	$76.90	5.239%	$80.9288	$80.93	$80.95	$80.90
7 purchase totals =	$730.90		$796.8346	$796.83	$796.85	$796.90