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	$87.64	3.467%	$90.6785	$90.68	$90.70	$90.70
Purchase #2	$167.74	13.614%	$190.5761	$190.58	$190.60	$190.60
Purchase #3	$43.57	11.153%	$48.4294	$48.43	$48.45	$48.40
Purchase #4	$128.52	7.849%	$138.6075	$138.61	$138.60	$138.60
Purchase #5	$198.59	3.495%	$205.5307	$205.53	$205.55	$205.50
Purchase #6	$10.59	13.801%	$12.0515	$12.05	$12.05	$12.10
Purchase #7	$134.25	5.650%	$141.8351	$141.84	$141.85	$141.80
7 purchase totals =	$770.90		$827.7088	$827.72	$827.80	$827.70