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	$18.85	13.867%	$21.4639	$21.46	$21.45	$21.50
Purchase #2	$13.25	5.657%	$13.9996	$14.00	$14.00	$14.00
Purchase #3	$67.48	4.527%	$70.5348	$70.53	$70.55	$70.50
Purchase #4	$220.46	9.606%	$241.6374	$241.64	$241.65	$241.60
Purchase #5	$59.93	7.823%	$64.6183	$64.62	$64.60	$64.60
Purchase #6	$81.88	13.397%	$92.8495	$92.85	$92.85	$92.80
Purchase #7	$131.68	12.820%	$148.5614	$148.56	$148.55	$148.60
7 purchase totals =	$593.53		$653.6649	$653.66	$653.65	$653.60