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	$200.82	10.719%	$222.3459	$222.35	$222.35	$222.30
Purchase #2	$38.26	10.145%	$42.1415	$42.14	$42.15	$42.10
Purchase #3	$102.76	11.412%	$114.487	$114.49	$114.50	$114.50
Purchase #4	$18.94	13.132%	$21.4272	$21.43	$21.45	$21.40
Purchase #5	$143.28	6.644%	$152.7995	$152.80	$152.80	$152.80
Purchase #6	$20.72	3.563%	$21.4583	$21.46	$21.45	$21.50
Purchase #7	$189.59	8.355%	$205.4302	$205.43	$205.45	$205.40
7 purchase totals =	$714.37		$780.0896	$780.10	$780.15	$780.00