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	$238.47	13.429%	$270.4941	$270.49	$270.50	$270.50
Purchase #2	$123.90	10.762%	$137.2341	$137.23	$137.25	$137.20
Purchase #3	$203.48	5.215%	$214.0915	$214.09	$214.10	$214.10
Purchase #4	$139.98	3.176%	$144.4258	$144.43	$144.45	$144.40
Purchase #5	$11.38	13.654%	$12.9338	$12.93	$12.95	$12.90
Purchase #6	$198.41	9.614%	$217.4851	$217.49	$217.50	$217.50
Purchase #7	$228.88	7.425%	$245.8743	$245.87	$245.85	$245.90
7 purchase totals =	$1,144.50		$1,242.5387	$1,242.53	$1,242.60	$1,242.50