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	$13.45	11.656%	$15.0177	$15.02	$15.00	$15.00
Purchase #2	$178.82	4.514%	$186.8919	$186.89	$186.90	$186.90
Purchase #3	$21.98	7.164%	$23.5546	$23.55	$23.55	$23.60
Purchase #4	$72.89	4.356%	$76.0651	$76.07	$76.05	$76.10
Purchase #5	$92.81	8.736%	$100.9179	$100.92	$100.90	$100.90
Purchase #6	$113.94	8.557%	$123.6898	$123.69	$123.70	$123.70
Purchase #7	$148.68	4.153%	$154.8547	$154.85	$154.85	$154.90
7 purchase totals =	$642.57		$680.9917	$680.99	$680.95	$681.10