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	$238.37	8.257%	$258.0522	$258.05	$258.05	$258.10
Purchase #2	$170.57	11.732%	$190.5813	$190.58	$190.60	$190.60
Purchase #3	$39.57	3.267%	$40.8628	$40.86	$40.85	$40.90
Purchase #4	$128.42	10.228%	$141.5548	$141.55	$141.55	$141.60
Purchase #5	$179.71	4.380%	$187.5813	$187.58	$187.60	$187.60
Purchase #6	$58.54	13.631%	$66.5196	$66.52	$66.50	$66.50
Purchase #7	$20.86	4.473%	$21.7931	$21.79	$21.80	$21.80
7 purchase totals =	$836.04		$906.9451	$906.93	$906.95	$907.10