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	$159.89	5.755%	$169.0917	$169.09	$169.10	$169.10
Purchase #2	$123.83	3.738%	$128.4588	$128.46	$128.45	$128.50
Purchase #3	$87.30	5.601%	$92.1897	$92.19	$92.20	$92.20
Purchase #4	$91.54	9.654%	$100.3773	$100.38	$100.40	$100.40
Purchase #5	$18.60	5.211%	$19.5692	$19.57	$19.55	$19.60
Purchase #6	$54.84	8.748%	$59.6374	$59.64	$59.65	$59.60
Purchase #7	$43.37	10.195%	$47.7916	$47.79	$47.80	$47.80
7 purchase totals =	$579.37		$617.1157	$617.12	$617.15	$617.20