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	$66.54	4.614%	$69.6102	$69.61	$69.60	$69.60
Purchase #2	$43.72	4.691%	$45.7709	$45.77	$45.75	$45.80
Purchase #3	$149.58	9.704%	$164.0952	$164.10	$164.10	$164.10
Purchase #4	$126.58	10.295%	$139.6114	$139.61	$139.60	$139.60
Purchase #5	$128.86	12.469%	$144.9276	$144.93	$144.95	$144.90
Purchase #6	$182.70	9.205%	$199.5175	$199.52	$199.50	$199.50
Purchase #7	$78.82	12.266%	$88.4881	$88.49	$88.50	$88.50
7 purchase totals =	$776.80		$852.0209	$852.03	$852.00	$852.00