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	$27.68	13.499%	$31.4165	$31.42	$31.40	$31.40
Purchase #2	$159.93	7.575%	$172.0447	$172.04	$172.05	$172.00
Purchase #3	$70.82	8.869%	$77.101	$77.10	$77.10	$77.10
Purchase #4	$78.64	5.370%	$82.863	$82.86	$82.85	$82.90
Purchase #5	$12.28	6.835%	$13.1193	$13.12	$13.10	$13.10
Purchase #6	$59.66	5.477%	$62.9276	$62.93	$62.95	$62.90
Purchase #7	$38.87	9.157%	$42.4293	$42.43	$42.45	$42.40
7 purchase totals =	$447.88		$481.9014	$481.90	$481.90	$481.80