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	$133.99	6.755%	$143.041	$143.04	$143.05	$143.00
Purchase #2	$126.36	12.748%	$142.4684	$142.47	$142.45	$142.50
Purchase #3	$109.71	6.628%	$116.9816	$116.98	$117.00	$117.00
Purchase #4	$162.35	4.350%	$169.4122	$169.41	$169.40	$169.40
Purchase #5	$36.55	10.829%	$40.508	$40.51	$40.50	$40.50
Purchase #6	$50.82	5.643%	$53.6878	$53.69	$53.70	$53.70
Purchase #7	$104.86	3.477%	$108.506	$108.51	$108.50	$108.50
7 purchase totals =	$724.64		$774.6050	$774.61	$774.60	$774.60