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	$91.99	9.378%	$100.6168	$100.62	$100.60	$100.60
Purchase #2	$38.48	9.710%	$42.2164	$42.22	$42.20	$42.20
Purchase #3	$28.34	12.484%	$31.878	$31.88	$31.90	$31.90
Purchase #4	$116.93	9.710%	$128.2839	$128.28	$128.30	$128.30
Purchase #5	$123.75	3.553%	$128.1468	$128.15	$128.15	$128.10
Purchase #6	$154.81	10.643%	$171.2864	$171.29	$171.30	$171.30
Purchase #7	$99.25	8.510%	$107.6962	$107.70	$107.70	$107.70
7 purchase totals =	$653.55		$710.1245	$710.14	$710.15	$710.10