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	$76.65	6.759%	$81.8308	$81.83	$81.85	$81.80
Purchase #2	$47.75	5.659%	$50.4522	$50.45	$50.45	$50.50
Purchase #3	$127.32	10.409%	$140.5727	$140.57	$140.55	$140.60
Purchase #4	$10.86	9.667%	$11.9098	$11.91	$11.90	$11.90
Purchase #5	$190.69	3.384%	$197.1429	$197.14	$197.15	$197.10
Purchase #6	$111.78	8.740%	$121.5496	$121.55	$121.55	$121.50
Purchase #7	$101.60	9.725%	$111.4806	$111.48	$111.50	$111.50
7 purchase totals =	$666.65		$714.9386	$714.93	$714.95	$714.90