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	$157.99	9.815%	$173.4967	$173.50	$173.50	$173.50
Purchase #2	$227.85	5.163%	$239.6139	$239.61	$239.60	$239.60
Purchase #3	$132.41	13.807%	$150.6918	$150.69	$150.70	$150.70
Purchase #4	$183.39	9.322%	$200.4856	$200.49	$200.50	$200.50
Purchase #5	$181.57	12.297%	$203.8977	$203.90	$203.90	$203.90
Purchase #6	$184.92	3.785%	$191.9192	$191.92	$191.90	$191.90
Purchase #7	$37.53	8.506%	$40.7223	$40.72	$40.70	$40.70
7 purchase totals =	$1,105.66		$1,200.8272	$1,200.83	$1,200.80	$1,200.80