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	$123.26	10.495%	$136.1961	$136.20	$136.20	$136.20
Purchase #2	$52.81	12.598%	$59.463	$59.46	$59.45	$59.50
Purchase #3	$62.80	5.813%	$66.4506	$66.45	$66.45	$66.50
Purchase #4	$97.82	8.764%	$106.3929	$106.39	$106.40	$106.40
Purchase #5	$36.29	11.335%	$40.4035	$40.40	$40.40	$40.40
Purchase #6	$203.60	11.255%	$226.5152	$226.52	$226.50	$226.50
Purchase #7	$89.55	11.873%	$100.1823	$100.18	$100.20	$100.20
7 purchase totals =	$666.13		$735.6036	$735.60	$735.60	$735.70