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	$35.79	13.607%	$40.6599	$40.66	$40.65	$40.70
Purchase #2	$163.28	7.238%	$175.0982	$175.10	$175.10	$175.10
Purchase #3	$203.39	6.373%	$216.352	$216.35	$216.35	$216.40
Purchase #4	$80.75	12.252%	$90.6435	$90.64	$90.65	$90.60
Purchase #5	$150.45	5.403%	$158.5788	$158.58	$158.60	$158.60
Purchase #6	$63.81	4.825%	$66.8888	$66.89	$66.90	$66.90
Purchase #7	$206.74	11.578%	$230.6764	$230.68	$230.70	$230.70
7 purchase totals =	$904.21		$978.8976	$978.90	$978.95	$979.00