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	$37.29	9.159%	$40.7054	$40.71	$40.70	$40.70
Purchase #2	$146.68	5.523%	$154.7811	$154.78	$154.80	$154.80
Purchase #3	$43.28	6.168%	$45.9495	$45.95	$45.95	$45.90
Purchase #4	$215.71	13.217%	$244.2204	$244.22	$244.20	$244.20
Purchase #5	$10.67	12.754%	$12.0309	$12.03	$12.05	$12.00
Purchase #6	$34.49	9.633%	$37.8124	$37.81	$37.80	$37.80
Purchase #7	$122.97	3.571%	$127.3613	$127.36	$127.35	$127.40
7 purchase totals =	$611.09		$662.8610	$662.86	$662.85	$662.80