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	$25.85	6.397%	$27.5036	$27.50	$27.50	$27.50
Purchase #2	$9.43	10.569%	$10.4267	$10.43	$10.45	$10.40
Purchase #3	$142.37	8.253%	$154.1198	$154.12	$154.10	$154.10
Purchase #4	$56.60	12.435%	$63.6382	$63.64	$63.65	$63.60
Purchase #5	$128.60	4.676%	$134.6133	$134.61	$134.60	$134.60
Purchase #6	$161.52	11.175%	$179.5699	$179.57	$179.55	$179.60
Purchase #7	$85.26	6.276%	$90.6109	$90.61	$90.60	$90.60
7 purchase totals =	$609.63		$660.4824	$660.48	$660.45	$660.40