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	$170.63	13.440%	$193.5627	$193.56	$193.55	$193.60
Purchase #2	$110.42	12.138%	$123.8228	$123.82	$123.80	$123.80
Purchase #3	$202.47	7.210%	$217.0681	$217.07	$217.05	$217.10
Purchase #4	$137.83	5.582%	$145.5237	$145.52	$145.50	$145.50
Purchase #5	$188.28	5.437%	$198.5168	$198.52	$198.50	$198.50
Purchase #6	$42.28	10.665%	$46.7892	$46.79	$46.80	$46.80
Purchase #7	$41.89	7.638%	$45.0896	$45.09	$45.10	$45.10
7 purchase totals =	$893.80		$970.3729	$970.37	$970.30	$970.40