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	$43.75	4.682%	$45.7984	$45.80	$45.80	$45.80
Purchase #2	$143.96	6.832%	$153.7953	$153.80	$153.80	$153.80
Purchase #3	$132.34	8.808%	$143.9965	$144.00	$144.00	$144.00
Purchase #4	$126.60	12.873%	$142.8972	$142.90	$142.90	$142.90
Purchase #5	$76.55	11.231%	$85.1473	$85.15	$85.15	$85.10
Purchase #6	$138.65	7.187%	$148.6148	$148.61	$148.60	$148.60
Purchase #7	$227.52	13.488%	$258.2079	$258.21	$258.20	$258.20
7 purchase totals =	$889.37		$978.4574	$978.47	$978.45	$978.40