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	$16.63	5.204%	$17.4954	$17.50	$17.50	$17.50
Purchase #2	$33.36	6.566%	$35.5504	$35.55	$35.55	$35.60
Purchase #3	$88.45	6.328%	$94.0471	$94.05	$94.05	$94.00
Purchase #4	$45.52	11.523%	$50.7653	$50.77	$50.75	$50.80
Purchase #5	$116.50	7.803%	$125.5905	$125.59	$125.60	$125.60
Purchase #6	$146.50	6.797%	$156.4576	$156.46	$156.45	$156.50
Purchase #7	$100.59	10.816%	$111.4698	$111.47	$111.45	$111.50
7 purchase totals =	$547.55		$591.3761	$591.39	$591.35	$591.50