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	$207.47	3.334%	$214.387	$214.39	$214.40	$214.40
Purchase #2	$83.43	8.387%	$90.4273	$90.43	$90.45	$90.40
Purchase #3	$160.25	12.776%	$180.7235	$180.72	$180.70	$180.70
Purchase #4	$89.43	4.631%	$93.5715	$93.57	$93.55	$93.60
Purchase #5	$245.86	3.274%	$253.9095	$253.91	$253.90	$253.90
Purchase #6	$58.83	3.832%	$61.0844	$61.08	$61.10	$61.10
Purchase #7	$41.55	8.517%	$45.0888	$45.09	$45.10	$45.10
7 purchase totals =	$886.82		$939.1920	$939.19	$939.20	$939.20