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	$149.58	4.288%	$155.994	$155.99	$156.00	$156.00
Purchase #2	$126.93	13.398%	$143.9361	$143.94	$143.95	$143.90
Purchase #3	$13.35	5.243%	$14.0499	$14.05	$14.05	$14.00
Purchase #4	$98.80	6.785%	$105.5036	$105.50	$105.50	$105.50
Purchase #5	$123.42	11.723%	$137.8885	$137.89	$137.90	$137.90
Purchase #6	$104.48	11.612%	$116.6122	$116.61	$116.60	$116.60
Purchase #7	$221.27	9.359%	$241.9787	$241.98	$242.00	$242.00
7 purchase totals =	$837.83		$915.9630	$915.96	$916.00	$915.90