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	$168.84	12.870%	$190.5697	$190.57	$190.55	$190.60
Purchase #2	$237.86	7.394%	$255.4474	$255.45	$255.45	$255.40
Purchase #3	$162.92	10.144%	$179.4466	$179.45	$179.45	$179.40
Purchase #4	$38.53	3.548%	$39.897	$39.90	$39.90	$39.90
Purchase #5	$19.93	4.788%	$20.8842	$20.88	$20.90	$20.90
Purchase #6	$197.33	7.748%	$212.6191	$212.62	$212.60	$212.60
Purchase #7	$79.84	5.855%	$84.5146	$84.51	$84.50	$84.50
7 purchase totals =	$905.25		$983.3786	$983.38	$983.35	$983.30