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	$125.99	13.119%	$142.5186	$142.52	$142.50	$142.50
Purchase #2	$40.85	6.713%	$43.5923	$43.59	$43.60	$43.60
Purchase #3	$99.92	13.406%	$113.3153	$113.32	$113.30	$113.30
Purchase #4	$27.68	6.641%	$29.5182	$29.52	$29.50	$29.50
Purchase #5	$47.34	8.328%	$51.2825	$51.28	$51.30	$51.30
Purchase #6	$133.65	3.733%	$138.6392	$138.64	$138.65	$138.60
Purchase #7	$208.67	6.784%	$222.8262	$222.83	$222.85	$222.80
7 purchase totals =	$684.10		$741.6923	$741.70	$741.70	$741.60