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	$104.83	13.214%	$118.6822	$118.68	$118.70	$118.70
Purchase #2	$102.84	6.324%	$109.3436	$109.34	$109.35	$109.30
Purchase #3	$166.50	7.733%	$179.3754	$179.38	$179.40	$179.40
Purchase #4	$142.52	12.840%	$160.8196	$160.82	$160.80	$160.80
Purchase #5	$115.40	13.548%	$131.0344	$131.03	$131.05	$131.00
Purchase #6	$57.69	7.159%	$61.82	$61.82	$61.80	$61.80
Purchase #7	$219.37	7.781%	$236.4392	$236.44	$236.45	$236.40
7 purchase totals =	$909.15		$997.5144	$997.51	$997.55	$997.40