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	$120.64	8.767%	$131.2165	$131.22	$131.20	$131.20
Purchase #2	$231.43	7.757%	$249.382	$249.38	$249.40	$249.40
Purchase #3	$50.66	13.253%	$57.374	$57.37	$57.35	$57.40
Purchase #4	$36.84	6.529%	$39.2453	$39.25	$39.25	$39.20
Purchase #5	$174.27	6.605%	$185.7805	$185.78	$185.80	$185.80
Purchase #6	$188.67	5.590%	$199.2167	$199.22	$199.20	$199.20
Purchase #7	$18.51	10.304%	$20.4173	$20.42	$20.40	$20.40
7 purchase totals =	$821.02		$882.6323	$882.64	$882.60	$882.60