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	$137.85	3.859%	$143.1696	$143.17	$143.15	$143.20
Purchase #2	$75.28	10.573%	$83.2394	$83.24	$83.25	$83.20
Purchase #3	$78.56	6.226%	$83.4511	$83.45	$83.45	$83.50
Purchase #4	$209.27	3.491%	$216.5756	$216.58	$216.60	$216.60
Purchase #5	$86.26	11.404%	$96.0971	$96.10	$96.10	$96.10
Purchase #6	$211.50	9.456%	$231.4994	$231.50	$231.50	$231.50
Purchase #7	$119.55	10.233%	$131.7836	$131.78	$131.80	$131.80
7 purchase totals =	$918.27		$985.8158	$985.82	$985.85	$985.90