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	$114.79	12.436%	$129.0653	$129.07	$129.05	$129.10
Purchase #2	$211.90	4.122%	$220.6345	$220.63	$220.65	$220.60
Purchase #3	$162.39	8.317%	$175.896	$175.90	$175.90	$175.90
Purchase #4	$100.48	11.318%	$111.8523	$111.85	$111.85	$111.90
Purchase #5	$44.85	13.273%	$50.8029	$50.80	$50.80	$50.80
Purchase #6	$203.28	5.345%	$214.1453	$214.15	$214.15	$214.10
Purchase #7	$231.89	3.549%	$240.1198	$240.12	$240.10	$240.10
7 purchase totals =	$1,069.58		$1,142.5161	$1,142.52	$1,142.50	$1,142.50