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	$225.97	6.117%	$239.7926	$239.79	$239.80	$239.80
Purchase #2	$176.46	5.748%	$186.6029	$186.60	$186.60	$186.60
Purchase #3	$194.84	13.811%	$221.7494	$221.75	$221.75	$221.70
Purchase #4	$120.69	13.321%	$136.7671	$136.77	$136.75	$136.80
Purchase #5	$100.60	7.806%	$108.4528	$108.45	$108.45	$108.50
Purchase #6	$174.51	12.551%	$196.4128	$196.41	$196.40	$196.40
Purchase #7	$74.57	5.510%	$78.6788	$78.68	$78.70	$78.70
7 purchase totals =	$1,067.64		$1,168.4564	$1,168.45	$1,168.45	$1,168.50