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	$23.56	13.786%	$26.808	$26.81	$26.80	$26.80
Purchase #2	$100.34	12.233%	$112.6146	$112.61	$112.60	$112.60
Purchase #3	$31.52	4.125%	$32.8202	$32.82	$32.80	$32.80
Purchase #4	$34.98	8.485%	$37.9481	$37.95	$37.95	$37.90
Purchase #5	$179.39	9.581%	$196.5774	$196.58	$196.60	$196.60
Purchase #6	$45.95	7.588%	$49.4367	$49.44	$49.45	$49.40
Purchase #7	$208.26	10.285%	$229.6795	$229.68	$229.70	$229.70
7 purchase totals =	$624.00		$685.8845	$685.89	$685.90	$685.80