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	$23.62	7.296%	$25.3433	$25.34	$25.35	$25.30
Purchase #2	$53.61	7.482%	$57.6211	$57.62	$57.60	$57.60
Purchase #3	$89.29	11.289%	$99.3699	$99.37	$99.35	$99.40
Purchase #4	$151.65	9.361%	$165.846	$165.85	$165.85	$165.80
Purchase #5	$126.61	13.585%	$143.81	$143.81	$143.80	$143.80
Purchase #6	$58.90	6.563%	$62.7656	$62.77	$62.75	$62.80
Purchase #7	$94.68	10.789%	$104.895	$104.90	$104.90	$104.90
7 purchase totals =	$598.36		$659.6509	$659.66	$659.60	$659.60