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	$199.59	4.660%	$208.8909	$208.89	$208.90	$208.90
Purchase #2	$193.42	11.338%	$215.35	$215.35	$215.35	$215.40
Purchase #3	$123.73	13.552%	$140.4979	$140.50	$140.50	$140.50
Purchase #4	$122.25	5.384%	$128.8319	$128.83	$128.85	$128.80
Purchase #5	$123.88	10.754%	$137.2021	$137.20	$137.20	$137.20
Purchase #6	$64.85	7.161%	$69.4939	$69.49	$69.50	$69.50
Purchase #7	$172.94	9.217%	$188.8799	$188.88	$188.90	$188.90
7 purchase totals =	$1,000.66		$1,089.1466	$1,089.14	$1,089.20	$1,089.20