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	$211.48	13.126%	$239.2389	$239.24	$239.25	$239.20
Purchase #2	$40.39	8.610%	$43.8676	$43.87	$43.85	$43.90
Purchase #3	$29.45	13.750%	$33.4994	$33.50	$33.50	$33.50
Purchase #4	$167.72	3.632%	$173.8116	$173.81	$173.80	$173.80
Purchase #5	$64.83	13.294%	$73.4485	$73.45	$73.45	$73.40
Purchase #6	$89.95	6.236%	$95.5593	$95.56	$95.55	$95.60
Purchase #7	$123.28	11.523%	$137.4856	$137.49	$137.50	$137.50
7 purchase totals =	$727.10		$796.9109	$796.92	$796.90	$796.90