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	$63.98	8.364%	$69.3313	$69.33	$69.35	$69.30
Purchase #2	$176.83	13.388%	$200.504	$200.50	$200.50	$200.50
Purchase #3	$9.63	9.445%	$10.5396	$10.54	$10.55	$10.50
Purchase #4	$143.26	7.611%	$154.1635	$154.16	$154.15	$154.20
Purchase #5	$34.44	8.874%	$37.4962	$37.50	$37.50	$37.50
Purchase #6	$139.32	4.184%	$145.1491	$145.15	$145.15	$145.10
Purchase #7	$47.90	3.106%	$49.3878	$49.39	$49.40	$49.40
7 purchase totals =	$615.36		$666.5715	$666.57	$666.60	$666.50