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	$114.31	8.128%	$123.6011	$123.60	$123.60	$123.60
Purchase #2	$223.29	11.302%	$248.5262	$248.53	$248.55	$248.50
Purchase #3	$212.25	7.839%	$228.8883	$228.89	$228.90	$228.90
Purchase #4	$238.51	7.561%	$256.5437	$256.54	$256.55	$256.50
Purchase #5	$20.74	13.104%	$23.4578	$23.46	$23.45	$23.50
Purchase #6	$123.60	3.604%	$128.0545	$128.05	$128.05	$128.10
Purchase #7	$204.75	3.827%	$212.5858	$212.59	$212.60	$212.60
7 purchase totals =	$1,137.45		$1,221.6574	$1,221.66	$1,221.70	$1,221.70