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	$137.48	13.117%	$155.5133	$155.51	$155.50	$155.50
Purchase #2	$100.34	5.422%	$105.7804	$105.78	$105.80	$105.80
Purchase #3	$196.81	12.476%	$221.364	$221.36	$221.35	$221.40
Purchase #4	$127.34	7.347%	$136.6957	$136.70	$136.70	$136.70
Purchase #5	$168.63	12.693%	$190.0342	$190.03	$190.05	$190.00
Purchase #6	$34.98	12.170%	$39.2371	$39.24	$39.25	$39.20
Purchase #7	$105.83	13.180%	$119.7784	$119.78	$119.80	$119.80
7 purchase totals =	$871.41		$968.4031	$968.40	$968.45	$968.40