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	$200.91	8.810%	$218.6102	$218.61	$218.60	$218.60
Purchase #2	$50.53	12.240%	$56.7149	$56.71	$56.70	$56.70
Purchase #3	$74.65	4.702%	$78.16	$78.16	$78.15	$78.20
Purchase #4	$32.48	6.161%	$34.4811	$34.48	$34.50	$34.50
Purchase #5	$117.58	11.631%	$131.2557	$131.26	$131.25	$131.30
Purchase #6	$192.33	6.832%	$205.47	$205.47	$205.45	$205.50
Purchase #7	$220.86	12.744%	$249.0064	$249.01	$249.00	$249.00
7 purchase totals =	$889.34		$973.6983	$973.70	$973.65	$973.80