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	$25.65	5.648%	$27.0987	$27.10	$27.10	$27.10
Purchase #2	$53.45	13.584%	$60.7106	$60.71	$60.70	$60.70
Purchase #3	$111.88	5.123%	$117.6116	$117.61	$117.60	$117.60
Purchase #4	$134.32	4.861%	$140.8493	$140.85	$140.85	$140.80
Purchase #5	$205.57	5.659%	$217.2032	$217.20	$217.20	$217.20
Purchase #6	$92.31	12.769%	$104.0971	$104.10	$104.10	$104.10
Purchase #7	$37.55	13.390%	$42.5779	$42.58	$42.60	$42.60
7 purchase totals =	$660.73		$710.1484	$710.15	$710.15	$710.10