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	$99.73	6.189%	$105.9023	$105.90	$105.90	$105.90
Purchase #2	$240.69	6.715%	$256.8523	$256.85	$256.85	$256.90
Purchase #3	$179.76	9.718%	$197.2291	$197.23	$197.25	$197.20
Purchase #4	$10.71	8.576%	$11.6285	$11.63	$11.65	$11.60
Purchase #5	$18.83	12.680%	$21.2176	$21.22	$21.20	$21.20
Purchase #6	$228.96	5.730%	$242.0794	$242.08	$242.10	$242.10
Purchase #7	$137.71	4.445%	$143.8312	$143.83	$143.85	$143.80
7 purchase totals =	$916.39		$978.7404	$978.74	$978.80	$978.70