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	$38.32	6.816%	$40.9319	$40.93	$40.95	$40.90
Purchase #2	$77.87	12.445%	$87.5609	$87.56	$87.55	$87.60
Purchase #3	$29.70	10.494%	$32.8167	$32.82	$32.80	$32.80
Purchase #4	$18.32	8.320%	$19.8442	$19.84	$19.85	$19.80
Purchase #5	$164.25	4.831%	$172.1849	$172.18	$172.20	$172.20
Purchase #6	$152.44	10.714%	$168.7724	$168.77	$168.75	$168.80
Purchase #7	$23.30	4.607%	$24.3734	$24.37	$24.35	$24.40
7 purchase totals =	$504.20		$546.4844	$546.47	$546.45	$546.50