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	$35.34	8.851%	$38.4679	$38.47	$38.45	$38.50
Purchase #2	$58.33	13.117%	$65.9811	$65.98	$66.00	$66.00
Purchase #3	$142.75	12.752%	$160.9535	$160.95	$160.95	$161.00
Purchase #4	$144.72	7.416%	$155.4524	$155.45	$155.45	$155.50
Purchase #5	$157.34	5.808%	$166.4783	$166.48	$166.50	$166.50
Purchase #6	$94.57	6.673%	$100.8807	$100.88	$100.90	$100.90
Purchase #7	$18.72	6.131%	$19.8677	$19.87	$19.85	$19.90
7 purchase totals =	$651.77		$708.0816	$708.08	$708.10	$708.30