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	$38.53	4.504%	$40.2654	$40.27	$40.25	$40.30
Purchase #2	$218.75	9.191%	$238.8553	$238.86	$238.85	$238.90
Purchase #3	$10.49	13.297%	$11.8849	$11.88	$11.90	$11.90
Purchase #4	$231.70	10.152%	$255.2222	$255.22	$255.20	$255.20
Purchase #5	$241.25	12.624%	$271.7054	$271.71	$271.70	$271.70
Purchase #6	$215.64	7.413%	$231.6254	$231.63	$231.65	$231.60
Purchase #7	$48.58	13.302%	$55.0421	$55.04	$55.05	$55.00
7 purchase totals =	$1,004.94		$1,104.6007	$1,104.61	$1,104.60	$1,104.60