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	$93.50	4.383%	$97.5981	$97.60	$97.60	$97.60
Purchase #2	$118.50	7.866%	$127.8212	$127.82	$127.80	$127.80
Purchase #3	$205.59	12.336%	$230.9516	$230.95	$230.95	$231.00
Purchase #4	$96.38	7.809%	$103.9063	$103.91	$103.90	$103.90
Purchase #5	$248.86	13.595%	$282.6925	$282.69	$282.70	$282.70
Purchase #6	$244.46	4.313%	$255.0036	$255.00	$255.00	$255.00
Purchase #7	$214.79	3.785%	$222.9198	$222.92	$222.90	$222.90
7 purchase totals =	$1,222.08		$1,320.8931	$1,320.89	$1,320.85	$1,320.90