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	$34.52	12.720%	$38.9109	$38.91	$38.90	$38.90
Purchase #2	$25.44	7.832%	$27.4325	$27.43	$27.45	$27.40
Purchase #3	$128.80	12.790%	$145.2735	$145.27	$145.25	$145.30
Purchase #4	$52.43	4.427%	$54.7511	$54.75	$54.75	$54.80
Purchase #5	$66.66	8.846%	$72.5567	$72.56	$72.55	$72.60
Purchase #6	$44.60	12.416%	$50.1375	$50.14	$50.15	$50.10
Purchase #7	$179.57	7.342%	$192.754	$192.75	$192.75	$192.80
7 purchase totals =	$532.02		$581.8162	$581.81	$581.80	$581.90