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	$13.68	12.636%	$15.4086	$15.41	$15.40	$15.40
Purchase #2	$90.39	5.669%	$95.5142	$95.51	$95.50	$95.50
Purchase #3	$72.28	5.177%	$76.0219	$76.02	$76.00	$76.00
Purchase #4	$148.96	6.484%	$158.6186	$158.62	$158.60	$158.60
Purchase #5	$163.25	13.677%	$185.5777	$185.58	$185.60	$185.60
Purchase #6	$156.85	12.695%	$176.7621	$176.76	$176.75	$176.80
Purchase #7	$176.35	11.634%	$196.8666	$196.87	$196.85	$196.90
7 purchase totals =	$821.76		$904.7697	$904.77	$904.70	$904.80