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	$89.83	11.606%	$100.2557	$100.26	$100.25	$100.30
Purchase #2	$80.81	11.377%	$90.0038	$90.00	$90.00	$90.00
Purchase #3	$111.28	6.162%	$118.1371	$118.14	$118.15	$118.10
Purchase #4	$37.28	13.439%	$42.2901	$42.29	$42.30	$42.30
Purchase #5	$27.37	8.310%	$29.6444	$29.64	$29.65	$29.60
Purchase #6	$121.64	5.864%	$128.773	$128.77	$128.75	$128.80
Purchase #7	$211.79	13.116%	$239.5684	$239.57	$239.55	$239.60
7 purchase totals =	$680.00		$748.6725	$748.67	$748.65	$748.70