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	$105.62	11.568%	$117.8381	$117.84	$117.85	$117.80
Purchase #2	$136.83	4.725%	$143.2952	$143.30	$143.30	$143.30
Purchase #3	$192.26	9.831%	$211.1611	$211.16	$211.15	$211.20
Purchase #4	$50.71	11.378%	$56.4798	$56.48	$56.50	$56.50
Purchase #5	$233.52	8.181%	$252.6243	$252.62	$252.60	$252.60
Purchase #6	$105.45	12.639%	$118.7778	$118.78	$118.80	$118.80
Purchase #7	$86.37	3.215%	$89.1468	$89.15	$89.15	$89.10
7 purchase totals =	$910.76		$989.3231	$989.33	$989.35	$989.30