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	$19.74	10.838%	$21.8794	$21.88	$21.90	$21.90
Purchase #2	$12.42	6.589%	$13.2384	$13.24	$13.25	$13.20
Purchase #3	$185.71	7.412%	$199.4748	$199.47	$199.45	$199.50
Purchase #4	$48.80	4.857%	$51.1702	$51.17	$51.15	$51.20
Purchase #5	$148.79	13.204%	$168.4362	$168.44	$168.45	$168.40
Purchase #6	$78.62	11.633%	$87.7659	$87.77	$87.75	$87.80
Purchase #7	$112.75	11.445%	$125.6542	$125.65	$125.65	$125.70
7 purchase totals =	$606.83		$667.6191	$667.62	$667.60	$667.70