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	$22.94	3.142%	$23.6608	$23.66	$23.65	$23.70
Purchase #2	$135.69	6.757%	$144.8586	$144.86	$144.85	$144.90
Purchase #3	$143.69	4.617%	$150.3242	$150.32	$150.30	$150.30
Purchase #4	$49.59	6.780%	$52.9522	$52.95	$52.95	$53.00
Purchase #5	$152.52	7.801%	$164.4181	$164.42	$164.40	$164.40
Purchase #6	$152.99	8.376%	$165.8044	$165.80	$165.80	$165.80
Purchase #7	$103.63	9.523%	$113.4987	$113.50	$113.50	$113.50
7 purchase totals =	$761.05		$815.5170	$815.51	$815.45	$815.60