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	$38.65	8.856%	$42.0728	$42.07	$42.05	$42.10
Purchase #2	$54.60	8.439%	$59.2077	$59.21	$59.20	$59.20
Purchase #3	$183.80	8.233%	$198.9323	$198.93	$198.95	$198.90
Purchase #4	$56.44	5.845%	$59.7389	$59.74	$59.75	$59.70
Purchase #5	$30.28	4.406%	$31.6141	$31.61	$31.60	$31.60
Purchase #6	$76.93	4.652%	$80.5088	$80.51	$80.50	$80.50
Purchase #7	$248.81	6.497%	$264.9752	$264.98	$265.00	$265.00
7 purchase totals =	$689.51		$737.0498	$737.05	$737.05	$737.00