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	$172.97	7.779%	$186.4253	$186.43	$186.45	$186.40
Purchase #2	$87.58	13.804%	$99.6695	$99.67	$99.65	$99.70
Purchase #3	$99.42	9.643%	$109.0071	$109.01	$109.00	$109.00
Purchase #4	$50.56	11.492%	$56.3704	$56.37	$56.35	$56.40
Purchase #5	$119.31	4.426%	$124.5907	$124.59	$124.60	$124.60
Purchase #6	$48.43	8.167%	$52.3853	$52.39	$52.40	$52.40
Purchase #7	$14.69	6.651%	$15.667	$15.67	$15.65	$15.70
7 purchase totals =	$592.96		$644.1153	$644.13	$644.10	$644.20