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	$24.79	11.682%	$27.686	$27.69	$27.70	$27.70
Purchase #2	$57.55	13.679%	$65.4223	$65.42	$65.40	$65.40
Purchase #3	$111.52	10.518%	$123.2497	$123.25	$123.25	$123.20
Purchase #4	$237.60	8.800%	$258.5088	$258.51	$258.50	$258.50
Purchase #5	$189.29	12.314%	$212.5992	$212.60	$212.60	$212.60
Purchase #6	$92.48	4.204%	$96.3679	$96.37	$96.35	$96.40
Purchase #7	$187.99	3.594%	$194.7464	$194.75	$194.75	$194.70
7 purchase totals =	$901.22		$978.5803	$978.59	$978.55	$978.50