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	$140.33	3.274%	$144.9244	$144.92	$144.90	$144.90
Purchase #2	$212.68	6.478%	$226.4574	$226.46	$226.45	$226.50
Purchase #3	$95.81	5.121%	$100.7164	$100.72	$100.70	$100.70
Purchase #4	$123.54	4.691%	$129.3353	$129.34	$129.35	$129.30
Purchase #5	$237.32	9.364%	$259.5426	$259.54	$259.55	$259.50
Purchase #6	$87.54	4.678%	$91.6351	$91.64	$91.65	$91.60
Purchase #7	$239.52	13.166%	$271.0552	$271.06	$271.05	$271.10
7 purchase totals =	$1,136.74		$1,223.6664	$1,223.68	$1,223.65	$1,223.60