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	$94.31	6.487%	$100.4279	$100.43	$100.45	$100.40
Purchase #2	$11.43	12.238%	$12.8288	$12.83	$12.85	$12.80
Purchase #3	$29.52	6.653%	$31.484	$31.48	$31.50	$31.50
Purchase #4	$83.94	3.103%	$86.5447	$86.54	$86.55	$86.50
Purchase #5	$109.80	10.132%	$120.9249	$120.92	$120.90	$120.90
Purchase #6	$246.78	13.792%	$280.8159	$280.82	$280.80	$280.80
Purchase #7	$38.42	10.830%	$42.5809	$42.58	$42.60	$42.60
7 purchase totals =	$614.20		$675.6071	$675.60	$675.65	$675.50