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	$89.98	9.444%	$98.4777	$98.48	$98.50	$98.50
Purchase #2	$137.42	3.426%	$142.128	$142.13	$142.15	$142.10
Purchase #3	$40.69	12.268%	$45.6818	$45.68	$45.70	$45.70
Purchase #4	$199.57	7.677%	$214.891	$214.89	$214.90	$214.90
Purchase #5	$11.59	13.267%	$13.1276	$13.13	$13.15	$13.10
Purchase #6	$90.47	13.426%	$102.6165	$102.62	$102.60	$102.60
Purchase #7	$29.82	4.231%	$31.0817	$31.08	$31.10	$31.10
7 purchase totals =	$599.54		$648.0043	$648.01	$648.10	$648.00