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	$104.70	11.161%	$116.3856	$116.39	$116.40	$116.40
Purchase #2	$197.82	8.334%	$214.3063	$214.31	$214.30	$214.30
Purchase #3	$83.29	7.440%	$89.4868	$89.49	$89.50	$89.50
Purchase #4	$57.95	6.602%	$61.7759	$61.78	$61.80	$61.80
Purchase #5	$107.95	4.550%	$112.8617	$112.86	$112.85	$112.90
Purchase #6	$148.55	12.332%	$166.8692	$166.87	$166.85	$166.90
Purchase #7	$221.32	4.802%	$231.9478	$231.95	$231.95	$231.90
7 purchase totals =	$921.58		$993.6333	$993.65	$993.65	$993.70