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	$113.39	13.547%	$128.7509	$128.75	$128.75	$128.80
Purchase #2	$108.79	8.306%	$117.8261	$117.83	$117.85	$117.80
Purchase #3	$143.40	12.526%	$161.3623	$161.36	$161.35	$161.40
Purchase #4	$39.91	8.818%	$43.4293	$43.43	$43.45	$43.40
Purchase #5	$26.48	11.476%	$29.5188	$29.52	$29.50	$29.50
Purchase #6	$185.88	5.382%	$195.8841	$195.88	$195.90	$195.90
Purchase #7	$103.28	7.592%	$111.121	$111.12	$111.10	$111.10
7 purchase totals =	$721.13		$787.8925	$787.89	$787.90	$787.90