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	$55.60	5.276%	$58.5335	$58.53	$58.55	$58.50
Purchase #2	$126.56	13.426%	$143.5519	$143.55	$143.55	$143.60
Purchase #3	$96.78	11.572%	$107.9794	$107.98	$108.00	$108.00
Purchase #4	$137.64	12.335%	$154.6179	$154.62	$154.60	$154.60
Purchase #5	$233.73	9.440%	$255.7941	$255.79	$255.80	$255.80
Purchase #6	$69.38	13.307%	$78.6124	$78.61	$78.60	$78.60
Purchase #7	$29.67	12.317%	$33.3245	$33.32	$33.30	$33.30
7 purchase totals =	$749.36		$832.4137	$832.40	$832.40	$832.40