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	$143.39	10.253%	$158.0918	$158.09	$158.10	$158.10
Purchase #2	$132.75	13.595%	$150.7974	$150.80	$150.80	$150.80
Purchase #3	$213.88	9.842%	$234.9301	$234.93	$234.95	$234.90
Purchase #4	$47.31	8.751%	$51.4501	$51.45	$51.45	$51.50
Purchase #5	$37.50	11.726%	$41.8973	$41.90	$41.90	$41.90
Purchase #6	$198.37	10.707%	$219.6095	$219.61	$219.60	$219.60
Purchase #7	$37.92	13.687%	$43.1101	$43.11	$43.10	$43.10
7 purchase totals =	$811.12		$899.8863	$899.89	$899.90	$899.90