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	$85.60	5.834%	$90.5939	$90.59	$90.60	$90.60
Purchase #2	$159.95	9.567%	$175.2524	$175.25	$175.25	$175.30
Purchase #3	$213.29	4.116%	$222.069	$222.07	$222.05	$222.10
Purchase #4	$87.92	5.628%	$92.8681	$92.87	$92.85	$92.90
Purchase #5	$89.76	10.779%	$99.4352	$99.44	$99.45	$99.40
Purchase #6	$40.70	3.126%	$41.9723	$41.97	$41.95	$42.00
Purchase #7	$236.49	10.580%	$261.5106	$261.51	$261.50	$261.50
7 purchase totals =	$913.71		$983.7015	$983.70	$983.65	$983.80