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	$247.59	3.490%	$256.2309	$256.23	$256.25	$256.20
Purchase #2	$71.73	13.120%	$81.141	$81.14	$81.15	$81.10
Purchase #3	$90.96	10.664%	$100.66	$100.66	$100.65	$100.70
Purchase #4	$49.53	13.600%	$56.2661	$56.27	$56.25	$56.30
Purchase #5	$132.65	4.360%	$138.4335	$138.43	$138.45	$138.40
Purchase #6	$100.78	5.685%	$106.5093	$106.51	$106.50	$106.50
Purchase #7	$220.38	10.694%	$243.9474	$243.95	$243.95	$243.90
7 purchase totals =	$913.62		$983.1882	$983.19	$983.20	$983.10