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	$136.70	4.260%	$142.5234	$142.52	$142.50	$142.50
Purchase #2	$100.87	6.307%	$107.2319	$107.23	$107.25	$107.20
Purchase #3	$238.38	13.105%	$269.6197	$269.62	$269.60	$269.60
Purchase #4	$152.71	3.386%	$157.8808	$157.88	$157.90	$157.90
Purchase #5	$51.56	4.713%	$53.99	$53.99	$54.00	$54.00
Purchase #6	$38.71	8.338%	$41.9376	$41.94	$41.95	$41.90
Purchase #7	$198.96	3.305%	$205.5356	$205.54	$205.55	$205.50
7 purchase totals =	$917.89		$978.7190	$978.72	$978.75	$978.60