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	$151.42	5.362%	$159.5391	$159.54	$159.55	$159.50
Purchase #2	$172.88	13.823%	$196.7772	$196.78	$196.80	$196.80
Purchase #3	$175.69	9.530%	$192.4333	$192.43	$192.45	$192.40
Purchase #4	$25.39	11.296%	$28.2581	$28.26	$28.25	$28.30
Purchase #5	$47.48	3.309%	$49.0511	$49.05	$49.05	$49.10
Purchase #6	$46.95	13.613%	$53.3413	$53.34	$53.35	$53.30
Purchase #7	$158.93	13.348%	$180.144	$180.14	$180.15	$180.10
7 purchase totals =	$778.74		$859.5441	$859.54	$859.60	$859.50