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	$206.95	11.771%	$231.3101	$231.31	$231.30	$231.30
Purchase #2	$93.79	6.531%	$99.9154	$99.92	$99.90	$99.90
Purchase #3	$152.65	5.361%	$160.8336	$160.83	$160.85	$160.80
Purchase #4	$78.48	10.681%	$86.8624	$86.86	$86.85	$86.90
Purchase #5	$93.64	6.105%	$99.3567	$99.36	$99.35	$99.40
Purchase #6	$45.86	6.159%	$48.6845	$48.68	$48.70	$48.70
Purchase #7	$172.63	9.503%	$189.035	$189.04	$189.05	$189.00
7 purchase totals =	$844.00		$915.9977	$916.00	$916.00	$916.00