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	$43.48	3.792%	$45.1288	$45.13	$45.15	$45.10
Purchase #2	$99.38	12.309%	$111.6127	$111.61	$111.60	$111.60
Purchase #3	$20.92	11.210%	$23.2651	$23.27	$23.25	$23.30
Purchase #4	$88.37	8.349%	$95.748	$95.75	$95.75	$95.70
Purchase #5	$46.48	4.668%	$48.6497	$48.65	$48.65	$48.60
Purchase #6	$150.41	7.337%	$161.4456	$161.45	$161.45	$161.40
Purchase #7	$11.62	11.682%	$12.9774	$12.98	$13.00	$13.00
7 purchase totals =	$460.66		$498.8273	$498.84	$498.85	$498.70