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	$91.33	10.114%	$100.5671	$100.57	$100.55	$100.60
Purchase #2	$105.73	12.202%	$118.6312	$118.63	$118.65	$118.60
Purchase #3	$134.99	9.729%	$148.1232	$148.12	$148.10	$148.10
Purchase #4	$63.50	11.285%	$70.666	$70.67	$70.65	$70.70
Purchase #5	$38.77	3.338%	$40.0641	$40.06	$40.05	$40.10
Purchase #6	$104.29	7.183%	$111.7812	$111.78	$111.80	$111.80
Purchase #7	$35.87	7.495%	$38.5585	$38.56	$38.55	$38.60
7 purchase totals =	$574.48		$628.3913	$628.39	$628.35	$628.50