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	$36.96	3.643%	$38.3065	$38.31	$38.30	$38.30
Purchase #2	$97.93	11.771%	$109.4573	$109.46	$109.45	$109.50
Purchase #3	$128.53	12.407%	$144.4767	$144.48	$144.50	$144.50
Purchase #4	$140.90	12.838%	$158.9887	$158.99	$159.00	$159.00
Purchase #5	$127.35	10.381%	$140.5702	$140.57	$140.55	$140.60
Purchase #6	$44.42	9.431%	$48.6093	$48.61	$48.60	$48.60
Purchase #7	$58.47	13.328%	$66.2629	$66.26	$66.25	$66.30
7 purchase totals =	$634.56		$706.6716	$706.68	$706.65	$706.80