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	$38.71	3.581%	$40.0962	$40.10	$40.10	$40.10
Purchase #2	$160.90	9.417%	$176.052	$176.05	$176.05	$176.10
Purchase #3	$249.41	6.747%	$266.2377	$266.24	$266.25	$266.20
Purchase #4	$184.67	8.382%	$200.149	$200.15	$200.15	$200.10
Purchase #5	$183.56	7.169%	$196.7194	$196.72	$196.70	$196.70
Purchase #6	$140.88	8.516%	$152.8773	$152.88	$152.90	$152.90
Purchase #7	$98.79	10.246%	$108.912	$108.91	$108.90	$108.90
7 purchase totals =	$1,056.92		$1,141.0436	$1,141.05	$1,141.05	$1,141.00