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	$49.82	5.300%	$52.4605	$52.46	$52.45	$52.50
Purchase #2	$160.46	13.325%	$181.8413	$181.84	$181.85	$181.80
Purchase #3	$128.81	12.255%	$144.5957	$144.60	$144.60	$144.60
Purchase #4	$120.39	12.555%	$135.505	$135.51	$135.50	$135.50
Purchase #5	$15.86	10.258%	$17.4869	$17.49	$17.50	$17.50
Purchase #6	$240.62	6.362%	$255.9282	$255.93	$255.95	$255.90
Purchase #7	$38.40	11.811%	$42.9354	$42.94	$42.95	$42.90
7 purchase totals =	$754.36		$830.7530	$830.77	$830.80	$830.70