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	$20.84	11.456%	$23.2274	$23.23	$23.25	$23.20
Purchase #2	$135.58	13.816%	$154.3117	$154.31	$154.30	$154.30
Purchase #3	$227.78	12.153%	$255.4621	$255.46	$255.45	$255.50
Purchase #4	$165.25	12.310%	$185.5923	$185.59	$185.60	$185.60
Purchase #5	$239.67	6.785%	$255.9316	$255.93	$255.95	$255.90
Purchase #6	$67.52	4.273%	$70.4051	$70.41	$70.40	$70.40
Purchase #7	$14.73	8.426%	$15.9711	$15.97	$15.95	$16.00
7 purchase totals =	$871.37		$960.9013	$960.90	$960.90	$960.90