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	$155.36	3.196%	$160.3253	$160.33	$160.35	$160.30
Purchase #2	$128.46	11.231%	$142.8873	$142.89	$142.90	$142.90
Purchase #3	$45.36	3.643%	$47.0125	$47.01	$47.00	$47.00
Purchase #4	$184.49	11.626%	$205.9388	$205.94	$205.95	$205.90
Purchase #5	$50.40	4.249%	$52.5415	$52.54	$52.55	$52.50
Purchase #6	$95.32	10.693%	$105.5126	$105.51	$105.50	$105.50
Purchase #7	$90.57	3.262%	$93.5244	$93.52	$93.50	$93.50
7 purchase totals =	$749.96		$807.7424	$807.74	$807.75	$807.60