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	$10.44	4.109%	$10.869	$10.87	$10.85	$10.90
Purchase #2	$43.57	6.638%	$46.4622	$46.46	$46.45	$46.50
Purchase #3	$128.64	9.672%	$141.0821	$141.08	$141.10	$141.10
Purchase #4	$167.26	3.380%	$172.9134	$172.91	$172.90	$172.90
Purchase #5	$146.75	9.546%	$160.7588	$160.76	$160.75	$160.80
Purchase #6	$94.64	6.176%	$100.485	$100.49	$100.50	$100.50
Purchase #7	$42.61	12.562%	$47.9627	$47.96	$47.95	$48.00
7 purchase totals =	$633.91		$680.5332	$680.53	$680.50	$680.70