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	$70.64	11.284%	$78.611	$78.61	$78.60	$78.60
Purchase #2	$23.25	9.477%	$25.4534	$25.45	$25.45	$25.50
Purchase #3	$74.78	10.621%	$82.7224	$82.72	$82.70	$82.70
Purchase #4	$48.98	3.776%	$50.8295	$50.83	$50.85	$50.80
Purchase #5	$133.88	7.142%	$143.4417	$143.44	$143.45	$143.40
Purchase #6	$238.73	13.187%	$270.2113	$270.21	$270.20	$270.20
Purchase #7	$61.50	11.264%	$68.4274	$68.43	$68.45	$68.40
7 purchase totals =	$651.76		$719.6967	$719.69	$719.70	$719.60