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	$123.30	5.733%	$130.3688	$130.37	$130.35	$130.40
Purchase #2	$199.33	7.201%	$213.6838	$213.68	$213.70	$213.70
Purchase #3	$75.28	4.672%	$78.7971	$78.80	$78.80	$78.80
Purchase #4	$192.25	11.781%	$214.899	$214.90	$214.90	$214.90
Purchase #5	$90.47	10.562%	$100.0254	$100.03	$100.05	$100.00
Purchase #6	$51.70	10.402%	$57.0778	$57.08	$57.10	$57.10
Purchase #7	$100.76	12.757%	$113.614	$113.61	$113.60	$113.60
7 purchase totals =	$833.09		$908.4659	$908.47	$908.50	$908.50